The Diamond is the first Windows Mobile phone to have an accelerometer. This lets the display automatically re-orient itself when you rotate the phone. Finally! Why didn’t someone think of this sooner? Oh yeah - Apple did.
The accelerometer functionality only works in some programs like Opera 9.5 and the photo application. It also works in the game Teeter, which allows you to move a ball around the screen by tilting the device. Pretty neat =D.