Basically you tell StumbleUpon what posts you like on different blogs, and it makes recommendations for new sites for you to check out. There is even a Thumbs Down, for sites that "aren't for you." It actually reminds me a lot of Pandora, if any of you use that!
If you want to follow me on StumbleUpon, my username is jbrobeck.
So if you like my post, click on the StumbleUpon box below! You are "recommending" my site to others with similar interests. But watch out - it's addicting!