[natabbotts]

Agreed. Knowing that the company requiring you to sign in can quite easily access all the data stored by Facebook worries me greatly. Twitter logins I have no problem with, as all my twitter info is public anyway (such is the nature of twitter), so there isn't any damage that can be done. Facebook, however, gives you no way of knowing exactly what it stores and shares, and because of this I am simply too paranoid to log in with it.

The best login system is OAuth by far - it is secure, and doesn't have any risk attached.