Facebook has begun to roll out a new mobile feature called Nearby Friends, which (as implied) notifies whenever your friends are in the vicinity. While this could be a recipe for privacy-related disaster - and Facebook has enough problems as it is already - users have already been told they can opt out of the feature. The app also lets users decide who can view your location, and those you pick can only do so if they allow you to view them too.
Hosting a number of other features, Nearby Friends allows you to share your specific location with a particular person for a set time period. You can also have filtered lists (like "Family" or "Close Friends"), or even share your location with the whole of your friends list. Nearby Friends can also be turned on or off, something that gives you full control. This seems pretty clear-cut and straightforward, and users should feel a lot more comfortable with Nearby Friends than the rest of Facebook's confusing privacy settings. Hopefully this will stand by the time Nearby Friends is rolled out to all Facebook users.