Social From the Ground Up
developers.facebook.com
developers.facebook.com
You're not going to see a startup get accepted that is essentially a competitor to Facebook -- it's too late for that. Even if it were, this partnership would give them the chance to know about the startup and acquire it long before it becomes a threat.
Really? In the recent video of Scoble interviewing pg pg mentioned that yc funded a privacy-oriented social network company that failed.
So I don't think a facebook competitor is out of the realm of yc funding.