Howtogeek posted a beginners guide about grouping similar applications using folders on your iOS 4 device

Do you have a lot of apps on your iPhone or iPod Touch and are tired of moving through screens to get the one you need? Here we look at a new feature in iOS 4 that let's you group apps together in folders.
Note: At the time of this writing, the folders option isn't available on the iPad, but will be included in the iOS update 4.2 (coming in November) and allow you to save 20 items in each folder versus 12 in the iPhone/Touch.

  Beginner: Group Similar Apps Using Folders on Your iOS 4 iPhone or iPod Touch