With only one exception, all the newly added privacy settings default to Only Friends, which is excellent. People should start off with privacy settings on, and then they can decide on their own whether they want to turn them off. That one exception is a big one, however, and it's one everyone should be aware of.
A quick recap: Facebook Places is a location-based service similar to Foursquare or Gowalla that allows users to "check in" to physical locations. You can check in at a restaurant, or a store and then let your friends know that you're there. If they're nearby, they can join you, or simply see where you've checked in. You can also view a newsfeed of where your friends have been and what they had to say while they were there. With Facebook's existing userbase of 500 million users, this has the potential to be huge and millions of people are already using it.
The one concern is in regards to allowing friends to check you in somewhere. The idea is that if you're at a concert, for example, one of your friends can check in, and check you in as being there, so you don't have to. Sounds like a good idea, but do you really want your friends to be able to post your location? Some people do, I'm sure, but if you don't, here's how to change it.
Log into Facebook, then click Account in the top right, then Privacy Settings. Now click Customize settings in the center and scroll down to the section called Things others share. The bottom option in that section says, Friends can check me into places. Change that to Disabled if you're concerned about that privacy detail.
That's it! This might also be a good time to double check all of your other privacy settings since you're there anyway. Now you can chose to use Places when you want to, and never worry about a friend checking you in without your knowledge.