I don't have a Facebook account, so I can't sign up. I think this is probably true of a lot of Bitcoin users--for a lot of Bitcoin users, Bitcoin is a way to stay off the grid, and being on Facebook would defeat the purpose.
My suggestion is to provide a way to sign up without Facebook.
Bitcoin... a monetary system that requires internet connectivity and CPU usage... in which every transaction is recorded forever and the database is replicated by all participants... is "off the grid"?
(Disclaimer : I'm a fervent Bitcoin supporter, I like its pseudonymous property and discard any anonymat claims. I've never used zerocoin because I don't have any use for it.)
While its true for a lot of Bitcoin users, one of our goals was to make bitcoin more accessible to the public and the average person who is interested in bitcoin but doesn't quite know how to get started.
Agreed that being on Facebook takes away anonymity, which is one of Bitcoin's benefits. There are also many great non-anonymous uses for Bitcoin- "free PayPal", for example. That's the angle we're taking in this app.
My suggestion is to provide a way to sign up without Facebook.