From the StumbleUpon news:
You can now integrate StumbleUpon with your blog, letting your visitors submit new articles directly from the page if they have a StumbleUpon account. This helps you get more traffic to individual articles, so they will spread faster within the StumbleUpon community.
So right news Digg it and del.icio.us, you can have your StumbleUpon social bookmark. Rand from Seomoz has some great info on what StumbleUpon trafic does for you.
If you’ll have a look at the social bar below, I have already integrated the “Stumble It” button.