Recently came across the AirMouse app for iPhone and iPod Touch and was blown away.People may dismiss it at first as it is $8.29 but the features are huge.

You have ability to fully control input of Mac or PC via the iPhone/Touch including accelerometer, touchpad, gestures, buttons, full keyboard etc. Has ability to be fully customisable as per the context of the application running at any time.

http://www.mobileairmouse.com/

Have a look at the demo to get a full appreciation of how it is used

Ideal for a Mac Mini or a Windows Media Centre in the lounge, or for using your Mac/PC for presentations.  Great for FrontRow on older Macs that do not have IR Port (or not wanting to pay for a Keyspan for FrontRow)

Currently communicates via Wifi, but will incorporate Bluetooth when iPhone 3.0 is available.