Nice. Compression rates vary greatly as I would expect from app to app. My BlitzMax debug builds of applications get a huge improvement in size, while others save a few megs here or there. I did not notice any slowing of loading applications once they were compressed and all have been behaving normally. (I did Mail.app to test as I have it running all the time.)
I could see this being useful in tandem with trim the fat and monolingual or a similar tool to save every last bit of space on a bootable backup or disc.
One feature I'd like to see is a report after an app is compressed of how much space was saved.