We are looking into Google/Linkedin Oauth. Not fans of Facebook, though...
-Simon, Stuff.li
I'd say it's a given that FB users also use Google, and would be just as likely to use either service's OAuth.
I tried to quickly find some numbers on distribution between them. Although I didn't find anything concrete, it seems to be Facebook > Google > LinkedIn. I would actually love to know more about this. Maybe someone with more experience has some more data?
/s