I participated in the ICFP 2003 contest (www.dtek.chalmers.se/groups/icfpcontest/),
joining a team of Rubyists. Even though we didn’t submit an entry in
the end, it was really fun, and very valuable (not to mention exhausting
:).
The main project lives (and dies) within a 72H time-frame, and involves
tight communication between people who had (in our case) never met before,
neither physically nor virtually. Problems arise naturally within a few
hours, and it is indeed from mistakes that one can learn the most.