Have to hand it to them; Anonymous Login is a genius name for their new service. Anonymous is the new black, and while this does have it, it also is logging into a service using Facebook.
Said another way, Facebook knows exactly what you’re doing; it’s just the apps that don’t.
This reminds me a bit of the GPL, in that it’s an open system which paradoxically grants rather more rights to the original creator than anyone else. In a similar way, Facebook still has the data, even if the target app doesn’t.
In the end, this is mostly about trying to allow for Facebook to enter into more arenas, and being an even larger point of control.
Truthfully, I find Anonymous Logins useful: there are a variety of services which I’d like to test drive, but I don’t because of the amount of information about me that they would get in the process.
In any case, this move is brilliant, and it defines a new standard for how to pitch data gathering services to people in today’s culture.