If you don't have one of the compatible Sony Ericsson phones (and a Bluetooth-enabled mac) you'll want to get one! Here are some ideas on what you may want to do with Sony Ericsson Clicker:

Control PowerPoint or Keynote when giving presentations.
Control DVD Player or iTunes from your sofa or bed.
Use AppleScript to control anything you like!

Further, Sony Ericsson Clicker has a built in "proximity sensor", allowing you to trigger actions when you leave or come back to your Mac. Again, here are some ideas

Pause iTunes when you leave the room, turn it on when you come back.
Use AppleScript to let your presence (or absence) control anything you like!

Jonas Salling Shareware - Sony Ericsson Clicker