So i've created the oauth-active-resource gem. With the help of some dynamic module/class generation magic, it's now as simple as it should be to create oauth/activeresource clients.
Have a look at the SoundCloud gem to find out how you can implement your own API wrappers based on the oauth-active-resource gem. If you've any questions feel free to contact me.
small bonus: Multipart file post to an active-resource
another bonus: I wrote a small script to sync rdoc documentation to a github project wiki.