This may be the ultimate Internet time-waster. Stumbleupon.com is a site where you enter your interests — politics, history, computer tips, whatever — and then you install the Stumbleupon tool bar to your Internet Explorer or Firefox browser. Clicking on the icon takes you to a random site in your area of interest. There’s more to the story, but that’s the basic idea. It’s great if you’re looking for a way to become totally unproductive for the day.