I am looking into solutions for providing multiple login methods to my site. I found rpxnow.com and they map user accounts from all the different networks. My question is how do they know that I am user1 on twitter and bigdude2 on facebook? I'm hoping it goes beyond email lookups.
The end result I want is a unique user in my database no matter what account they sign in with, dupes are a no-no, but most likely inevitable I am guessing.