Continuously grooming your list of people who've wronged you requires a lot of upkeep and thought. Let Unfriend Finder help you out by keeping track of the people who ditch you as a friend on Facebook.
Photo by Pete (yourspleen)
(Click to enlarge.)
There's nothing terribly surprising or complicated about installing and using Unfriend Finder. You just download it, install it in your web browser of choice (assuming your choice is either Chrome, Firefox, Opera or Safari), log into Facebook, and let Unfriend Finder do its job. It's important to note it's not retroactive, so you're not going to find a bunch of lost friends just by installing it. Instead, install it now, be patient, and wait for certain "friends" to drop you thinking you won't notice. You will, and you'll be able to remind them of their indiscretion some day.
Unfriend Finder for Facebook [Userscripts]