For an app that allows user to login in with Facebook, and will support scenario where friends can be involved, should the app automatically setup the connection within the app's context? Such that for user A and B who are friends on facebook, and both logged in the app with their Facebook account, the app will automatically treat them as friends in the app's social graph.
It depends on your apps nature.
For example on Foursquare, if one of your friend started to use the Foursquare through facebook, they send you a notification stating that
Ohhh! Looks like your Facebook Friend XXX is on Foursquare. Friend them?
and another app DrawMyThing, automatically connect you with your friend and involve your friend in your activity automatically.
So what important is the nature of your app.
