Are you familiar with the Android Account Manager? [1] You can let users log in to your app with pretty much one click of an existing account. Since virtually every android user already have a google account signed in on their phones. It seems that using a google account would be the most obvious route for ideal user experience (no need to type in a new account you haven't before).
That's funny, I'm the opposite. I'm generally unlikely to sign up for any site or service that makes me create and record yet another username/password combo.
It seems there's a discussion on your forum now. [1]
Unfortunately, to chime in on the discussion one needs to log in with Facebook, which might keep a good chunk of those 'Please support something else' voices out. I know you wrote (both here and in that entry) that you plan to support other authentication methods. The reason why I post this is just to point out the flaw of asking the subset that willingly gives out their FB details in the first place.
(besides creating a dedicated account)