There are lots of other things... I can customize themes, wallpapers for springboard and lockscreen, rotating wallpapers, 5 icons on your dock, etc. as far as aesthetics go. Also, I can hide icons for apps I don't use much, like iTunes, compass, calculator, and the native stocks app. Obviously iOS4 will have folders so one could technically dump all of these into one or two 'junk' folders . I also can use my phone as a temporary hard drive when I jail-break it, in that I can store files on its hard drive. Essentially, like a large flash drive.

This is just scratching the surface, though. There are lots of others, like an app that lets you control/manage torrents remotely, an app that allows you to basically firewall your phone (selectively block/open ports), an app that lets you run wifi-dependent programs on 3G, an app that lets you blacklist phone numbers, an app that downloads youtube videos, etc.

Allegedly, iOS4 has already been jailbroken and unlocked (in the beta form anyway).