A better question would be, for those of you who implement OpenID, Facebook Connect, etc. What's the customer percent breakdown against doing it the old fashioned (email & password) way?
In fact, a ton of the code that runs the site itself is fully open source: http://developers.facebook.com/fbopen/ That's mind-blowingly impressive. I still don't believe more people don't know about this or seem to care.
"FB connect" is a session management and authentication product from facebook. I find it obnoxious. It is pretty much literally the antithesis of openid. FB open source: good, FB connect: horrible.