Facebook's location features will include Foursquare-style checkins
Some code for a "location" tab in the touch.facebook.com version of the site seems to indicate checkins are coming, and also that Facebook's GPS accuracy might be even better than Foursquare's or Gowalla's.
The checkin system will use HTML5's location attribute, and not every browser supports that yet, so Facebook might just roll out checkins to mobile versions of the site at first. The location code includes latitude and longitude [no way! -Ed], as well as a measurement of how accurate your location is. I'm not sure how Facebook plans to measure accuracy, but it would be a trump card to play against other location services.
Hopefully, Facebook will allow other apps to access its location features via API, so you can pass existing Foursquare and Gowalla checkins to FB, and vice-versa.