One of things that's severely under-utilized on my Macbook is the Bluetooth module. This is scandalous really because Bluetooth is a fantastic option to have at your disposal, removing the need for cables when connecting external devices, especially mobile phones.
One of the cool little features of Bluetooth on Macs is that it allows you to control your machine via your mobile phone. Why on earth you would want to do this is another question but I guess it could be useful for presentations, if you've lost your remote control, or if you just want to play a trick on an unsuspecting user as they see their mouse cursor fly across the screen apparently of its own accord.
The following instructions are for a Sony Ericsson K750i but the same principles should apply to all Bluetooth enabled mobile phones:
1. Activate Bluetooth on both the Mac and phone
2. Select "Setup Bluetooth device..." from the Bluetooth menu
3. Depending on the capabilities of your phone, you'll be asked by the phone what you want to set it up for. I was offered the opportunity to set it up both as a data device and remote control
4. Make sure you accept the petition to use as a remote control on your mobile. Select "Accept" on your phone when you're ready to start and off you go!
What you'll then see on your phone is is a map of functions on your screen:
There is no keyboard so you can't type but you can browse the Internet on your Mac using the mobile phone to move the cursor (which moves rather sluggishly) and click on links. You can even shut down your Mac using your phone.
What's really impressive is the range - I was using the phone from 5 meters away and it was still working which would make it ideal for presentations. If you were to connect a device with a proper keyboard too (such as a Blackberry) you'd even be able to type, although I wouldn't want to try this for long!