I'm in a wedding this fall that's tux-less, so that's REALLY nice. I'll probably wear one of my own suits, but they aren't having everyone wear matching tuxes and dresses.
I'd like to second this idea. For our wedding, we had all the guys wear a black suit - didn't have to match. They had to get a matching shirt and tie, but they were fairly neutral and fashionable so that they can still use them at work. For the ladies, they all wore their own black dresses - also didn't have to match. Figure every guy should have a black tux, every gal has a black dress, and everyone was much more comfortable in their own clothes rather than paying out the rear for something they only wear once. Looking back at our pictures, you have to point out to people that the clothes didn't match.
To anyone getting married, this is my biggest recommendation.