Now that Facebook Places has been turned on, users who are uncomfortable with sharing their locations with Facebook friends should consider going through their privacy settings and making sure they aren't sharing more information than they are comfortable with.
Personally, I'm not interested in broadcasting my location via the Internet to everyone I know, or even a subset of people I know, so I've locked down my Facebook privacy settings. The "Places" feature is a pretty prominent one on the new mobile versions of Facebook (both in the iPhone app and in the Android browser), and I imagine it might be easy to accidentally use.
For those of you who are interested in turning Facebook Places off, here's how to do it. Log into Facebook. On the home screen, click on "account" and then "privacy settings."
In the middle of the page you'll see the words "customize settings." After clicking on this link you'll see the page where you can manage who can see all of your posts, photos, videos, personal information and other stuff. There are three items related to the new "Places" feature.
Under "Places I check in" I believe the default setting was "friends only," meaning your friends can see where you are but not anyone else. Clicking on this box shows you a few options, including one that lets everyone in the world see your Places activity. Since there is no obvious way to block everyone from seeing Places activity, you need to click the "custom" link and edit your custom privacy settings so that Places information is available to "Only Me." On this page you can also hide your Places information from certain people or lists of friends.
Next, you'll see an option that says "Include me in 'People Here Now' after I check in," which means other people will see where you are if they are "checked in nearby." Because Facebook typically makes default settings as public as possible, this option is pre-enabled. You have to uncheck the "enable" box to turn it off.
Finally, scroll down a little bit to the "Things others share" category and disable the part that says "Friends can check me in to Places."
As far as I can tell, doing these three things will limit your public broadcasting of information related to Facebook Places as much as is possible under Facebook's current privacy settings. Of course, Facebook has been forced to change its privacy settings before so this may not be the last word on the subject.