Leigh Dodds produced a well written survey of REST and social software intersections. I use the term intersection since many of the services described, the usual suspects, implement the REST philosophy less than completely. Dodd's also discusses some best practices for building such systems in a RESTful fashion.
I ran across this article from Lucas Gonze's detailed examination of Webjay and REST. It's a good look at one developer's real world set of design choices.