WhereMyFriends is an interesting application of facebook that will show you the geographical location of your friends on a Google Earth Map.
You have to connect your facebook account with this application and within one or two minutes application will fetch the location of your friends and shows them on the Google Map.
If you want to see the information of any friend, just click on that pin and you will get their name.
One disadvantage for this is, you can not keep it private. It is public and you can't change this setting. Every one can also see your friends list and their place or location.
You can see this example.
It is the usable and interesting application for the users of facebook. Share it with your friends.