[goldenthunder]

This could affect Facebook in a negative way. Think about big sites that get spammed with tons of fake email user accounts. Making Facebook registration the only option, these spammers will be forced through Facebook first, which just hurts Facebook. (Or do they want that so they can report a larger than accurate userbase? heh)

[gojomo]

I think Facebook wants that problem – but not to inflate their user numbers, rather to become better at pruning their system, improving it as the one true-life identity authority.