Facebook is apparently testing a feature called "Smart Lists" which appears to group your friends by people you work with, people you attend school with, and people who live within 50 miles of your current city.
The feature appears to have been first spotted by Nick Starr, who tweeted the following screen shot:
Update: Mashable has some additional screenshots of some broader friend-flitering testing.
The extent of the testing is unclear, and this may or may not become a mainstream feature, but it kind of seems like another way Facebook is encouraging users to use Facebook in a way that has made Google+ appealing to its users - the separation of friends.
Of course, it's not like Facebook didn't let you separate people before. Google's version was hardly a new idea. Facebook has had lists and groups both for some time, but this appears to be more a pre-made set of likely lists that users would want to use, without the user having to make the effort of setting them up.
The real appeal of Google's Circles as it launched was the ease of the Circle-specific sharing functionality. It's easy to know who you're sharing a post with at any time. Apparently recognizing this as a good idea, it didn't take Facebook too long to implement similar controls.
Facebook has also been reaching into the Twitter idea pool again lately as well. Check out the recent iOS app changes.