Not much has changed. I'm currently working to open source an implementation I worked on that's compliant with the finalized version of the spec. The most up-to-date implementation I've seen in the open is https://github.com/hiidef/oauth2app, which implements draft 16.
https://github.com/hasgeek/lastuser was the least painless method in my experience but I never tried any non-lastuser clients with it so I can't comment on library compatibility.
I've moved up to draft 22. The OAuth2 spec is now final, but I haven't been keeping track of what's changed. The final revisions seemed to be all around SAML.
Serious thanks for releasing this - it's been great to work with and really enjoyable to use as an entire platform for auth. We integrated it with our own openID service but great to have the functionality there if we want to open it to other sign-ons. Are you expecting any major changes once OAuth2 is final?
