From DOTRIGHTS.ORG:

If you want to use the privacy controls that are available, here’s how to do so.

Adjusting Check-In Visibility, Turning “Friend Check-Ins” and “Here Now” Off

1. Go to your privacy settings page and select “customize settings.”
2. Select the Places settings.
3. Enable Places? (You may need to enable the product before you can change your settings.)
4. Adjust your settings:
   1. To adjust who can see your check-ins, use the pulldown next to “who can see my location.”
   2. To disallow friend check-ins, uncheck the “Allow friends to check-in” box.
   3. To disable Here Now, uncheck the “Here Now” box
5. If you want, disable Places.

Preventing Your Friends’ Apps From Receiving Your Places Info

1. Go to your privacy settings page and select “edit my settings” under the “Applications and Websites” title.
2. Select “edit settings” next to “info available through my friends.”
3. Uncheck the Places check-in box.