Can't find this question on the forums, though the forums are hard to search.
I've installed "Social" by mailchimp / crowd favorite and it works so far, except: when I try to login ("sign in") as my facebook or twitter ID, it pops open the login page for those sites, lets me log in, and then closes that page. Then I'm back on my blog post, but the "sign in with facebook" or "sign in with twitter" buttons are still there.
I'm not signed in. The comment form is blank and if i fill it out and submit, it posts as my wordpress account with that avatar.
The same two accounts are connected to my blog user account, and when I sign in as that user, I can post either as facebook or twitter with no problems.
Mailchimp email support was helpful but directed me to these forums when the questions got beyond their scope.