I've been using FB auth only for a year or so on one of my Android apps. It's centered specifically around social sharing and I'm focusing on US based users at

I've been using FB auth only for a year or so on one of my Android apps. It's centered specifically around social sharing and I'm focusing on US based users at first. Given the maintenance tradeoffs around other login methods, I'm pretty happy with my choice. I'm sure that I lose groups of users that are only on Twitter, or Orkut or choose your SN du jour, but in the spirit of keeping things lean I'm happy with my choice. One can always add other auth methods when growth looks like a hockey stick. 500MM+ FB users should be enough to get started.