Here's a nice trick to take iSight snapshots from your Apple machine whenever someone registers a failed login. Whether your wife's trying to break into your machine to read your emails to your mistress, or some punk's made off with your MacBook Pro when you weren't looking, knowing who was trying to access your data is pretty darn useful.
You can even set the computer to automatically upload the pictures to an FTP so you can track the thief remotely. Though if you're anything like us, it'll probably be full of pictures of yourself (see Adam of Lifehacker) in various states of confusion as you fat finger your way to a failed login once again.
Take iSight snapshots during invalid login attempts [Mac OS X Hints via Lifehacker]