Stumble Upon is a website service and browser add-on that helps you find and share great web content. It's loads of fun in just a few clicks. You tell Stumble Upon what you like. You tell it your interests, hobbies, etc and it helps you find websites and content you might enjoy. I've never run into anything 'bad' stumbling, maybe a bit strange and irreverent, but never pornographic or very offensive. Due to the unpredicatbility of Stumble I would say, it's not a kids toy. Stumbling is not like websurfing or searching because you have no control over where you are going or even the topic. Stumble just randomly shows you sites of interest and you can thumbs up or thumbs down them to narrow your Stumbling. This info lets Stumble know what you like and offers you similar sites or what you don't like and it won't show you that again. Warning-it can be a bit addictive seeing what you might Stumble Upon next.
A fun feature is that you can subscribe to your friends Stumbles and see their favorites. You can find me on Stumble Upon at mitchellfamily. I mostly like (thumbs up) art, poetry, and educational resources.
I added the Stumble add-on to my firefox browser. It's pretty handy up there. It has a little SHARE button so you can easily email the page you are looking at or add it to your Facebook or Twitter status.