Do you ? I do. It's my new addiction. ^_^
How do I know? Here's a check list --

1. If you didn't Stumble Upon at least 10 sites, you didn't feel like you used the internet for the day.
2. Addictive games or activities on the internet catches only 10 seconds of your attention, afterwards, you keep on stumbling.
3. You don't surf anymore, you only stumble upon.
4. You keep a browser window just to 'stumble'.
5. You click on the Stumble! button to reload the page.