I want to build a location based app, so naturally I am going to write my app using an existing API. But I am not sure what the pros/cons of developing on top of Foursquare (or Gowalla) vs Facebook Places.
Note: this is not intended as a political debate "which service is cooler/better/sexier/whatever" but a true concern as to the pros and cons of using the facebook platform vs the others.
Edit for additional info: the app will basically want to add a "hook" that runs some of my code when a user checks in somewhere