When circumstances dictate it then I'll wear a suit and feel happy enough, but I much prefer casual wear (despite it being half past two in the morning here in Blighty I'm still dressed in jeans and a Scott Pilgrim t-shirt, the one with the Titanium Baseball Bat (+1 Against Blondes) scene).
Interesting fact, the last time I wore a suit that wasn't for a job interview was at my university summer ball at the end of my first year (in my third year now). It was more of a music festival over one evening, hosted by the university and some fancy estate on the outskirts of Leeds, yet everyone still had to wear evening dress as a dress code. It also happened to be on the rainiest night of the year, despite being the start of July, and this is really bad rain even by British standards. Combined with the grass all the music tents were set on, and thus plenty of mud, and the fact that to leave there was a massive queue for each coach back to university, me and my friends were like drowned rats. There were people at the medical tent with borderline hypothermia, one of my friends even had to go and warm up with those foil cloaks and everything, she was that cold...
Yeah, suits probably aren't a good mix with music festivals, even when they're touted as 'balls'...