All the results I've heard about have been mediocre. Besides, the FireFox SU toolbar now shows which sites are sponsored, so people will know.

With SU traffic you have to be really good at capturing their attention. I mean, the whole interface is designed for people with short attention spans, as far as I can tell.

Why not put a Stumble This link in your blog posts, or enlist your Twitter followers once in a while to thumb up your posts? Organic stumbling brings me a fair bit of traffic. (Like I did for one of your posts, and this post.)

While I've never tested SU paid advertising, I've submitted several articles to SU which has made me a believer in its ability to drive traffic. In just a two-week period, I was getting thousands of visitors to one of my sites months after I submitted the content. SU continues to work well after you submit content. I haven't had the same success with Digg or Reddit.