I think a dating service built on top of Facetime (again, with karma) would be pretty neat. Sort of like virtual speed-dating. Meet random people that meet your "requirements" and get to know them. Upsell: Give out the app for free, but limit connection times and all connections are anonymous (but reporting is not). Paid app lets you maintain an address book and unrestricted connection times.
Alternatively, those with the "free" version of the app are branded as such (i.e., your connecting partner is told that you are a cheapskate), providing social pressure to show that you're willing to spend money to meet interesting people.
Policing the system is probably the hardest part - setting up the social conditions such that fraudulent claims are kept to a minimum (and require little to no input from the service owner) is a challenging task.
You could even monetize by interspersing ads into the video stream.
In fact that could be a better solution - that way you could avoid building an application and locking yourself to iPhone 4 users, opening your web service to other FaceTime clients.
However, I assumed lots and lots of others would think the same, and I was VERY wary of Apple pulling some kind of censorship rejection BS with it.... So I abandoned the idea within seconds.