Like many others, my home screen is a collection of the apps I use the most. There is some thinking behind the placement of some of the apps, but not all. For example, the iPod app is located top right because that is the most comfortable way for me to access my music while my iPhone is connected in the car. My most used apps are in the dock with the row above it also getting heavy use.
Every few months I demote or promote an app and update my home screen. Possible promotions right now include Ember, Ramp Champ and iBank.
Some selected apps: