From http://oauth.net/about --
"Who is Going to Use it?
If you are a web developer – you, we hope. At the time of writing this, we expect implementations from (in alphabetical order) Digg, Jaiku, Flickr, Ma.gnolia, Plaxo, Pownce, Twitter, and hopefully Google, Yahoo, and others soon to follow."
"Google APIs accessible via OAuth
Google Data API documentation (Apps, Base, Blogger, Calendar, Code Search, Contacts, Finance Portfolio, Health, Notebook, Spreadsheets, Picasa Web Albums, Documents, Webmaster Tools, YouTube, etc.)
Documentation on OAuth Authentication for Web Applications and Using OAuth with the Google Data API Client Libraries
Using GData from Gadgets"