The problem I find with these techniques (like the one implemented on Ouibounce or the one proposed by Hristo Georgiev) is they also detect when the mouse enters the window if the cursor is outside the page before page load. It's not a big deal, but it might bring an unwanted behavior. An extra tweak must be done for this solution to work fine. One thing that comes to my mind right know would be to use a flag to check the mouse logic.
