This is very sad. I just submitted my application for Winter 2010 yesterday and just begun to learn about Hacker News, participate, .. and Boom!
I read about Dan and find out how a great guy he was and that he has committed suicide. This is an unlucky first sad impression for me and this forum, but it also has served, by reading through all your comments, to quickly find out what a tight and supportive community the YCombinator crowd is. My condolences to all those who knew him.