Facebook Places is, from what I've read, similar to foursquare, which is a more sophisticated version of someone tweeting where they are at any given moment.
For those of you who enjoy living in the now and don't mind the whole world (or the large portion or small portion you have friended through your social networking accounts) to know where you are (restaurants, concerts, bars, malls, etc) and where you aren't (home, so thieves have a better idea of knowing when to strike), Facebook Places will be another fun way to keep in touch with your friends and the world.
Call me a stick in the mud...
For those of us who are more wary and enjoy more (as opposed to less) privacy, the thing to know about the new Facebook Places is that even if you don't use the new feature, your friends can "tag" you into their Places updates to let everyone they know where you are.... And aren't. To remove the option (of giving away your location) from your fun loving and free spirited friends you need to go into your Facebook privacy setting and set your account to "disable."
This post on Gawker shows you how to do this step by step :)