We're looking at providing some live peer to peer video in sections of our site and have been playing with the API from Justin.TV for a couple of weeks now. There are some alternatives like Ustream and Livestream, but JTV looks like the only free platform with an open API.
Development has been smooth for basic stuff like broadcasting and consuming video feeds and the price is right so I can't complain, but support is limited and there are not many developer resources when you get into the rest of the API.
There is lightweight API documentation here, with a few examples:
There is a Google Group here, although activity is very limited:
Is anyone else in the SO community using JTV?