I think the parent poster should probably have emphasized the importance of HATEOAS more and the power hypertext/linking gives you. I won't spend any time on it in this comment since there are plenty of resources on the web for that, but that's really been the important thing about REST for me. It really is a wonderful thing that clients cannot even attempt invalid state transitions, and I don't think I've seen it done in any other even moderately popular RPC/IPC framework. In other frameworks/architectures for RPC/IPC all operations are just "available" all the time, but if you were to actually attempt to invoke them you'd get "operation not supported" (or the like).

Strangely, very few people (at least that I've spoken to) who are fans of REST seem to have even picked up on the HATEOAS principles. I'm guessing that their fandom is more predicated on a hatred of SOAP/XML and love of the simplicity of JSON -- which is kind of strange since HATEOAS also works beautifully for Content-type=XML over HTTP.

EDIT: An attempt to formalize the Richardson Maturity Model (L3) for REST+JSON/HTTP can be found at: http://stateless.co/hal_specification.html (I'm not affiliated with it in any way, just thought it was interesting.)