Bottom line, jailbreaking gets you control of your iPhone. Sure you can change wallpapers now with iOS4, but jailbreaking can get you a complete theme. Plus there are apps both paid and free that let you do things Apple would never dream of letting you do, like more app icons on a page, adding more icons to your dock. More icons in a folder. The list goes on and on. Like DannyBoy said, "Google is your friend!" Go check it out, you might be surprised.