So I've been toying with some AppleScript and a little application called Proximity (download) which gives you some pretty neat features. Currently I've got things set up to start the screen saver and require a password to wake it when my phone moves out of bluetooth range. When I come back into range it unlocks the screen saver and sets it to no longer require a password.
Big deal I hear you say, what if the situation was as such - you come home from mowing the lawn and when you walk through the door your music starts playing and your computer announces that while you were out you've received 4 new e-mail messages. Taking this a small step further you could, with the addition of some hardware, have the garage door open as you pull up the driveway, have the lights turn on and have the shades on your windows close. Of course this could all happen automatically in reverse when you leave the house.
What a way to spend a holiday weekend right?