The only benefit of anonymous facebook login over a native session is the supposed "cost" of creating too many accounts, and enabling things like a http://en.wikipedia.org/wiki/Sybil_attack

Actually I would like to ask if anyone here knows of more good solutions for making creating accounts expensive. Captchas ain't it anymore.

The best one I know is Phone Verification. http://www.blackhatworld.com/blackhat-seo/making-money/59699...

Buying a cellphone in order to get an account is expensive enough. But is there something better?