I have had my macbook for five years now and just recently ran applejack on my computer. It deleted five gigs of useless files, hence I was very pleased. My girlfriend was having problems with speed on her macbook and I decided to run applejack. Shortly after running applejack with no problems her computer, previously having no problems, would not boot past the grey apple logo screen and would shut down after trying for five min. I tried running it in safe mode (which it wouldn't do), tried every booting option I could thing of short of reinstalling OSX and deleting everything. After running it in single user mode and trying to repair the disk the problem surfaced. Her catalog files were corrupted. Thought I should let you know since I'm sure many people are downloading it as I speak.