There are so many many gorgeous things you could wear to a wedding that *aren't* black, I don't see the need to go with basic black.
Plenty of hip and classy dresses are out there in pretty colors, and black has just never seemed festive enough (to me) for a wedding. Besides, if all the trendy folks are wearing black, wear something different and wonderful and start a *new* trend. I consider myself fairly fashionable, and I'm definitely young (23), and I'd never wear a black cocktail dress to a wedding. Note: black with flowers or a pattern or something is ok, I think.
Just my semi-conservative anti-black-at-weddings $0.02.
~Greekgrrl