AirBnB also were friends with the Justin.tv guys so they were already "in the mafia" a bit :). Though if they sucked I'm sure PG would have said for them to fuck off.

That said, AirBnB had a large enough vision that even if there was a 95% chance of them bombing, the 5% chance of them rocking it was too big to pass up.

Given how tight the global startup community is, I imagine a lot of YC applicants are friends with YC founders.

AirBnB sold cereal. That is determined and imaginative anyone would fund them.