Facebook makes a big land grab for local data: they will be partnering with local businesses to gate wifi with a check in. So when you go to a coffee shop, instead of having some cryptic password of the day written on a whiteboard, you’ll instead see a Facebook login. If you want to use their wifi, then you’ll have to check in on Facebook and post it to your wall.
The bigger implication is that for most people who leave themselves logged in to Facebook, they might be getting very fine grained location data on you even if you don’t log in (much like they have done with the Like button on webpages). And if you do log in, the local business gets a plug from you to all your friends on Facebook, while Facebook gets a solid pinpoint of where you are to more accurately localize ads.