We're not quite sure why it wasn't included in the launch update, but the Facebook app for the PS Vita is now available in the US PlayStation Store. While we weren't blown away by the interface or functionality, it works well enough and doesn't cost a penny. It's also one of the more productive ways to use your Vita's rear touchpad, which is otherwise somewhat in need of software support right now. There's still no sign of the Foursquare app that hit Europe yesterday, though, which is a little puzzling. Adding Facebook outside of the regular weekly PlayStation Store updates would seem to suggest either that not everything was quite pulled together in time for launch, or that Sony is taking a slightly more liberal approach to adding store content than it has in the past. In any case, we'd expect Foursquare to show up soon.