Facebook app for Windows Phone 7 now supports Places and photo tagging
Facebook Places is Facebook's check-in system and it's now fully available inside the WP7 app. You can check-in from the app, see who else has checked in at the same location, browse through location-based deals -- the whole shebang.
Tagging people inside photographs is probably one of the many reasons for Facebook's popularity, and this ability is now built into the WP7 Facebook app as well.
Facebook for Windows Phone 7 is a free download or update from the Windows Phone 7 Marketplace.