Just thought I'd mention that I tried the social connect plugin that you recommend.
It worked perfect, apart from the fact it kept putting an underscore in the username when logged in via facebook etc which meant you kept getting a 404 error when viewing the author profile.
I posted a fix here - http://forums.appthemes.com/404-erro...15/#post183033
Another issue I had and still have is that when it does log you in - it shows you are logged in on the tool bar at the top but still shows the login page, even with redirect set to show dashboard or any other url.
The only way to get around this is to refresh the browser, then it works.
no other plugins installed - so for me, it doesn't work.