Who has unfriended you on Facebook?
By default Facebook doesn't let you see previous friends who have taken you off their lists. This can be a pain in the arse if say, you have a large number of friends and your friend-count goes down. Very tricky to keep track of who doesn't like you any more. Fret not my unpopular one, for help is at hand.
The aptly named Unfriend Finder is a third party utility which can be plugged into the Greasemonkey Firefox extension.
The Gory Details..
Unfriend Finder is a realtime script that informs you which of your erstwhile 'friends' removed you on Facebook. A local database keeps record of your friendlist and is compared at each refresh. Nifty.
Unfriends (you may have another name for them) are people who were previously your friend but have either deactivated their account or have removed you from their friendlist. The script will tell you which friends have removed you, who has deactivated their accounts, people you have requested friendship with and who has declined your friend request. Mwah-hah-hah-ha..!
Unfriend Finder even uses Facebook notification to alert you of these events. It makes identifying the unfriends (sounds a bit like 'the undead') easy by displaying a red counter in the menubar with the amount of unfriends you have - so it's not for use by those of a nervous disposition.
Note that the script cannot tell you which profile(s) had you on their friendlist before it was installed as it's not retroactive.