Don't know I applied as a team and still got rejected, ummm passed over. Should I take that more personally :-). Actually they have quite a tough job to do in reviewing so many applications. I the e-mail was actually almost too nice. It would have been helpful if it had some quantitative data as in what each person thought of it as in. As in a score or something even such as, we liked you but your idea really stunk, or no technical co-founder, or don't give up your day job.
Actually open call here. I am very interested in hearing any ideas that didn't get accepted. I hope to modify my site in the next day to allow a discussion on this and to talk to others. Y-combinator is a great way it seems to develop concepts, but not the only way. If other rejected ones are like us then we should really talk to each other. Feel free to e-mail me at joshua.smith@i4edge.com. Better yet here post on this page http://www.i4edge.com/ycombinator-apply-list/