WALRUSCP This app has a great developer behind it. I was the one (or one of the ones) who discovered the blacklist bug fixed in 1.7.2, and throughout the process the developer was pleasant and responsive.
As for Xslimmer itself, it has claimed untold MBs on my MacBook's hard disk, working as advertised. Occasionally you run across an application that gets screwy after slimming, but that's what the back-up and restore options are for. Most apps that will be troublesome when slimmed are on the blacklist.
Overall, this is a very easy to use app that is a must-have for mac owners who need to squeeze as much memory as possible out of their hard drive. Highly recommend it!
(Version 1.7.2)