If you visit stardust game website, you will find a Facebook like this
I was thinking about working on a social network based game.. so what better place to start than at the good and not so old facebook. I started looking at the documentation and was able to figure out what has to be done in a few minutes and i have to attribute it to the documentation. It is really good, there are a lot of examples all along with the docs. Registering the app was very simple too (was kinda worried that it would be something like the apple app store kinda review process). If you want to integrate FB in your site, just go to developers.facebook.com and you will know what to do.
And as for the integration... i've integrated my stardust game with facebook as in.. you can brag about your achievements in game on facebook from the game itself (i.e, if you allow the application to). Check it out here,