I've taken photos at two weddings, and one was my own (rimshot).

A friend of mine, back in the late '90s, knew I'd just recently started enjoying photography and invited me to be the "candid" photographer at his wedding, while the pro did his thing. He'd take the fancy posed shots, and I'd be right there to capture (for instance) the bride's expression when they were finally able to relax. While he was arranging family members and guests for group portraits, I was roaming the crowd catching what was going on... wedding street photography style. In fact, I think I was the only one who managed to get a shot of the cake before a friend of the bride unwittingly cut herself a piece and started chowing down... and I got a shot of the bride dressing her down as well.
I really enjoyed the relative freedom, and the ability to be a part of the party compared to the pro, and there wasn't a whole lot of pressure on me to produce technically superior photos, either.

It felt good, though, to discover that most of the photos that ended up in their wedding scrapbook were mine, taken with a lowly Canon EOS Rebel X. (see... I eventually got to the point!)

The marriage lasted about a year.