They have a wordpress plugin to post to twitter and/or facebook on each post you make using the su.pr link shortner and you can use your own domain for the short url. Plus they give you all sort of click and track information about the su.pr links.
You can also enable the StumbleUpon toolbar, so they can stumble your post easliy.
I’ll give it a try for awhile and see if it increases SU traffic.
Leave me a comment and let me know if you’ve tried it or what you think about it.