Well, I just sorta participated in one...didn't get too far, mainly because it conflicted with a graduation I had to attend and an interview for a job... but that's a different story.
I don't think there are any official ones coming up for a while, so I was wondering if some of the people here might be interested in doing an unofficial one in July sometime? I could check interest at some other forums I visit, it could be a pretty fun thing.
Lemme know!
http://www.scottmccloud.com/inventions/24hr/dare/dare.html for info
(Yea, I posted this thread at CAD forums too, I just wanted to spread the idea around).