With the web applications I've been building during the last years, I often had to think hard about my "Facebook policy". If you have any chance of virality, the Facebook platform can at least double it (I guess that the multiplier is much higher, actually).<p>The first time I considered creating an integration with FB, though, I studied how it worked and stopped when I discovered that I could NOT get my users' email [note: I think this isn't true now, I didn't really check though]. That meant that even those users that came directly to my website, but wanted to login using facebook, wouldn't have really become "my" users, that I would have always been dependent on FB.<p>Facebook changes its policies very often, so this particular problem could not be current anymore, but the fact remains that we should be very careful in helping a company which is building the biggest walled garden on the internet by adding too much value to it. Because now the gates are open, but FB can close them whenever they see fit.<p>Right now I'm considering again creating an integration with Facebook for one of my new services, but I'll try as hard as possible to steer the users to my actual website, even if this wouldn't be as frictionless as it could be for them. Bigger issues are at stake.