The most worrying aspect of Facebook Places is that you can be checked in by other people. So if you're skipping work, for example, and having lunch with a friend instead, they can check you both in and your boss could see it and fire you.
Fortunately, you need to opt-in to that privacy setting. The first time someone tries to check you in, you'll get an option to not allow them to do so or to allow other people to check you in. But once you approve one, you'll approve all future friend check-ins.
Thanks but no thanks, Facebook. Actually -- forget the first thanks, just no thanks. The last thing I need is some "friend" checking me into places thinking it'd be funny. *checks Superficial Writer into gay club like a million times*