The new iOS 4 operating system has a lot of improvements, but in my experience so far the most useful one is definitely folders.  Folders allow you to group a lot of apps together into a subgroup and helps you save a lot of space on your various screens.  I went from having 9 screens full of apps, to now just having 4.  It also helps you keep like items together if you choose to organize them that way.  Now, when I need access to an app related to my business, I just go to the Business folder and they’re all right there.