you can completely change your theme. Here are some examples.
Mac OSX Theme:
http://modmyi.com/forums/attachments...s-ipad-008.png
http://modmyi.com/forums/attachments...s-ipad-010.png
glass orb
http://img820.imageshack.us/img820/259/ipad1.png
and many many more, including
video wallpapers.
YouTube - Video wallpaper for ipad
More settings and toggles so you can modify everything on your iPad.
Emulators! You can play some of your favorite oldschool games on it!
(check this video out of playing Mario Kart 64 using a WiiMote)
Mario Kart 64 For Nintendo 64 On iPad Using Wiimote
Multitasking! you can use backgrounder with pro-switcher to have a palm Pre-like multitasking experience.
and other reasons as well