The BlackBerry End Call / Red Button (to the right of the Track Ball/Pad) is more than just for disconnecting a call and turning your phone on and off.
When you are in any application, you can press the End Call / Red Button and you will be taken back to your main screen.
You can then use any other application.
When you click on the application you left when pressing the End Call / Red Button you will be taken back to exactly the same place you were when you left that application.
This tip works only when you are not on a phone call.
Please remember that if you are ever on a phone call and you press the End Call / Red Button the call will be disconnected.