Some numbers I saw in a study that several have posted on Twitter:

Widget provider Gigya sent us some numbers from their social network login tool and in a three company competition, Facebook came away with 65% of the traffic, Myspace with 18% and Twitter with 17%.

Compared With Twitter & Myspace, Users Choose Facebook Login 2-to-1

MySpace has more than Twitter?  I smell a severely skewed survey.   Who is Gigya?  There has to be some unusual representation of MySpace users involved there,  because I see no way that MySpace has more than Twitter.  Which,  in turn,  says to me that this whole analysis is suspect. 

Who is Gigya anyway?  Where are their widgets found?

One commenter raised a good question:  How many of these users even have more than Facebook IDs?  A related question I would have is that among those with both Facebook and Twitter accounts who use both frequently,  how many of those use Facebook and how many use Twitter?