Facebook is careful to mention the privacy ramifications of this. First of all, you can only tag people you are friends with on these check-ins. Also, by default, your check-ins will only be visible to people you’re friends with (though you can change this to be visible to everyone). You can also opt-out of having friends be able tag you in a location updates. This is found in the privacy page.
I still haven’t had time to go through all the announcements, but they are partnering with Gowalla, and Foursquare for this as expected. Great to see they are taking privacy seriously right away, the problem with Facebook is that everyone is friends with each other, which defeats the purpose.