I'd rather base my opinion of YCombinator on the opinions of those who have actually gone through the program and have an insight and perspective about the program that are much more objective than any outsider's. If there's anyone who'd claim that joining YCombinator is a stupid idea, it'd be those who were actually put through the process.

However, I do have to say, that being rejected from YC and being an outside observer, I do at times feel that YC itself seems to get a bit 'clubby.' One big reason for this feeling comes straight out of pure envy and jealousy for wanting to be a YC member. The other reason deals with the fact that I feel as if the connections/information gained through such a program are ones that no one on the outside has access to. So it's either you're in and you're connected, or you're out and left in the dark.