Anyone got any idea what the directory names in /Applications that contains the .app is based on?

For example, I can find AIM.app at /Applications/7EF478D0-9F4E-46C9-8D90-3D0D2B9E8AE8/AIM.app

Cheers.

Apple split up the applications into the /Applications dir in root for the stock apps (and 3rd party ;-)
and the AppStore apps will go into the user dir under /var/mobile/Applications.

The cryptic dirs underneath are obviously related to the iTunes account.. because you can't exchange the apps with other users. Your device has to be activated for the iTunes account that purchased/loaded the app. So, if you copy that dir that you mentioned to another iPhone that was not synced with your iTunes (and your account) it wouldn't run.