Now most French couples have two wedding ceremonies:

First they go to the town hall with a relatively small group of family and friends. The bride wears a simple white dress or pantsuit. There the mayor, or a deputy mayor, reads aloud a decree of marriage, makes a few inspiring comments, announces the name and occupation of the bride, groom, parents and witnesses (the best man and maid of honor). Papers are signed with a fancy pen, and people clap. The guests file downstairs, or outside as the case may be, and photos are taken as the couple descend the staircase (there usually is one).
Secondly the couple go to the church. Now traditionally the church ceremony takes place later that same day, although it is also common to have that ceremony several weeks or even months later. This time the bride dresses up in white gown, hat or veil, gloves, etc. Already married by the state, this time they are married by the church (enevitably Catholic, although not required).
After the ceremony, those guests who also received an invitation to the reception (not guaranteed), meet at the parents' house or other large reception hall around 6:00pm for cocktails in the couple's honor. Those who are also invited for dinner, stay for a large feast around 9:00 pm with as many courses as possible, followed by dancing until 3:00am to 6:00 am.
The biggest change nowadays is that most French people are no longer devout Catholics. Marriage is no longer a duty or even necessary. One in two children in France is born "out of wedlock" now, and I can affirm that while 80% of our coupled friends have children, only 10% are married, and half of those marriages happened after a baby was expected. Even presidential candidate Ségolène Royale is not married to the father of her four children, and it has not been the subject of one newspaper article in France.
So for my personal experience, I will start with the wedding of about a month ago, in Versailles.
F. and I. are 29 and 31 years old. They've been together for at least 6 years. They bought a house together about a year and a half ago, and 7 months ago announced that they were expecting a baby. He works in computers, she is a maternity nurse. About 1 month after the baby was announced, they also mentioned their engagement to be married. The marriage, I gathered, was an afterthought, to make life simpler for the child, grandparents and great-grandparents, although there has never been any question about their love and devotion to each other.
Around February, they casually mentioned that they would be getting married in late March. Luckily most of us "friends" were free that weekend. There were no official invitations, and we had to ask they day before what time the ceremony would be. There was no bachelor party, no gift registration, and no official word on what would follow the ceremony.
We arrived at the mairie of Versailles exactly at 11:30 am on a Saturday, fearing we would be late, only to see the bride and groom pull up behind us and look for a parking space. We met the rest of the 15 or so invited friends and family on the steps of the town hall and took photos of the couple in the lobby. We filed up the grand staircase, arm in arm with our significant others, and waited in the upstairs hall for the wedding before ours to finish and leave the ceremony room.
We all entered and sat in the blue velvet Louis XVI chairs, oohing and aahing at the gold-trimmed, sculpted woodwork around the room. The couple entered on the arm of one of their parents. The groom in a black suit, the bride in a cream pantsuit. The mayor wore the traditional tri-color sash. The couple sat in the front row, facing the mayor (back to us), with their witnesses at the side, and their parents directly behind. The mayor spoke of duty to the family, of the history of the room we were in, and the tradition of leaving the door open to let anyone who might want to protest the marriage enter. The couple exchanged rings, kissed, and we all clapped. The names, birthdates and occupations were read aloud and the couple and witnesses were called up to the podium to sign the papers (the only part where they faced the audience).
We all cheered at the end (the whole thing took about 15 minutes), and we went up to congratulate the couple and their parents. Then we went downstairs and waited with cameras for the couple to descend the staircase.
Afterward we discovered that we were invited back to the parents' house after dinner for the second part of the evening. So after throwing rice on the couple as they exited the mairie, we all went our separate ways.
That evening we met at the parents' house and found the remains of a large feast. Only the close family had been invited for dinner, and now they had all gone out and left the couple with friends their own age. So we ate leftovers and drank champagne and had quite a civil party with 15 or so people until about 2:00am. The couple will have the church wedding, and presumably a honeymoon, next year sometime, after the baby is born and Maman is feeling better.
The second wedding we attended recently was a bit different in spirit...
A. is a stone sculptor and D. is some sort of engineer. Both are the children of agricultural families from the small villiages that dot the Alps behind Grenoble in southeast France. They've been together at least 5 years, living together for at least 3, and had a baby girl almost 2 years ago. We received the invitation to their wedding and bachelor/ette parties a few months ago.

This time the wedding at the mairie was the only one, since the couple are not religious. We did not attend the bachelor/ette party because we were at the Versailles wedding that weekend! (see above). But for the wedding we carpooled with two other friends for the 6 hour drive, pushing 110 mph for the last 45 minutes of the trip, to arrive (again) exactly at the hour requested. Fortunately, (again) the wedding did not start exactly on time. We arrived at 4:00 pm and found one of the last parking spaces along the streets of the sloping mountain villiage of some 200 inhabitants. We followed the sounds of children up the hill and arrived at the tiny building that was the town hall. A crowd of what must have been 100 people were there, all laughing, greeting with kisses and trying to keep hold of their (collectively) 25 babies and children running everywhere.

Some were in suits, others in birkenstocks and shorts. All had visibly put on something more formal than usual, and everyone looked comfortable. The bride wore a 1970's vintage-looking gown made by her cousin, with orange and green flower trim. The groom and best man wore a sharp white suit with lime green shirt and orange tie.
As the crowd swelled to 150 and everyone had taken pictures of everyone, the mass of people shuffled into a room built to hold 70 people. The couple sat in front, with their parents behind, and finally the windows had to be opened so that those still outside could see in and hear the proceedings. Children tried to stay still, and mostly succeeded, excepting two rogue cousins with balloons that climbed on chairs and posed for cameras behind the mayor, as he continued with the ceremony.
There was no microphone, and only half of the room could see or hear what was said, but the mayor, obviously a friend of the family, joked about the presidential election and the two candidates for marriage presented here before him. I didn't even really see the rings exchanged, or the papers signed, but when they kissed and turned around a wild cheer shook the tiny building, followed by quite a few children crying. I think the best part was the giant close-up of a rooster (symbol of France) on the wall behind the mayor. It had a fog of breath as it must have been a cold day, and the whole thing reminded me of Rocky (the rooster?).

People squeezed out of the room afterward and immediately began filling glasses and serving pizza squares under the tents set up just outside. 6 cookie sheets of home made pizza and 4 cookie sheets of home made hord'oeuvres were served along with bags of chips, pretzels and peanuts. 2 milkpails of home made rum punch were emptied, along with 3 bottles of Ricard and countless bottles of Coke and juice. Everyone chatted and ate and drank for almost 2 hours while kids ran back and forth and the newlyweds made their rounds. Most of us ended up sitting on the pavement in the sun while any heeled shoes that had been worn were promptly kicked off.

After 8 strong men returned from saving a car that had rolled into the stream, everyone who was left helped clean up everything and leave the place as we found it, and we got into cars to go to the dinner reception.
As the sun set behind the mountains, the last people arrived for the real party which was held at a camper's hostel that had been rented for the occasion. The Our Lady of Tirelire hostel is a two storey building with a dining hall, kitchen and some 130 bunkbeds upstairs . Five long tables were filled with home prepared food, and nearby stood 2 kegs of beer, 2 barrels of wine and the rest of the punch. Another room had tables and chairs, one corner with a laptop and speakers and flashing lights, and a dancefloor space had been reserved in the middle.

Photos of the whole family and friends were taken, and around 8:30 everyone took a plastic plate and attacked the food. Since there weren't enough chairs, the 140 some guests sat anywhere they could. It was cold outside in the mountain air, but not freezing, and most people had already abandoned suits and skirts for jeans and sneakers.

The music was eclectic but energetic, and everyone danced. Around midnight 15 bottles of champagne were poured into plastic goblets and one gigantic chocolate cake and 6 strawberry cakes were served. I must admit I took a nap for an hour or two on one of the upstairs beds in order to last the night, but when I returned around 2:00am the dancing was more fervent than ever. Most of the older adults had left, and the young families had put their kids to bed in some of the private rooms upstairs. Around 4:00am the bride and groom disappeared, but around 5:30 they were discovered passed out on the lawn in separate sleeping bags. The groom made a reappearance and managed to stay on his feet until just before dawn.
Around 6:00am the last 15 or so of us were witness to the pot de chambre. I hear that traditionally it is a toast to the couple of some sort, and they drink from the same cup, but here the bride's brother put together an evil concoction of leftovers and tramped out to the lawn to wake up the bride and make her drink it. She had a sip and survived, while her husband didn't fare so well. The rest of us quickly ran off to the safety of the bunkbeds before we had to try some too.
The next day was sunny and warm. Babies splashed in a kiddie pool on the pavement. Dogs roamed. Children played. Everyone drank coffee and ate leftovers on picnic tables. The last people left at 3:00pm.

So, I guess that people are the same everywhere really. Weddings are formal or relaxed, religious or not. But a theme I find in France so far is: why not get married so that we can have a party?