Remote control your computer
Some people are keen on the idea of using cellphones as a remote control. After all they are usually around, have a small size, a nice display and even some of them have an illuminated keyboard.
Among the choices for interfacing with another equipment, Bluetooth seems to best choice: more standard than infrared and lower power requirements than wifi (besides not many phones have IR or wifi).
Around this concept of using your Bluetooth cellphone as a remote was created AnyRemote project. I've tried lately for a home project and I'm very happy with this suite. Yes, it is actually a more complex system than I expected: You cellphone needs a special program to act as a remote, this program in written in Java and you need to download it to your phone. Then server software is installed in your computer and a set of configuration scripts tell your computer what to do when each key is pressed. On the other hand, user menu is provided on cellphone display (there is even a midnight commander file manager). Brilliant!!