I was just watching PG's Office Hours: http://www.justin.tv/startupschool/b/298808297 and at around 28:40 he has an insight that is almost word for word from our 2009 application: make a tool that targets the busybody matchmakers to circumvent the chicken and the egg program with dating sites. Don't make a dating site, just make a tool for matchmakers.
I guess the lesson here is that if you have a good idea, 10^n people have also had the same idea, 10^(n-2) are working on it right now and 10^(n-3) have a decent shot of making it work.
I was wondering, though, out of interest, how many other people have had the same experience of being unsuccessful with their YC application only to find their idea being touted, or, more gallingly, another team being accepted into YC with the same idea?