So I click the thumbs up for stumble everytime I write an article. Since July 7th I have written about 7 articles and about 3-4 pages, and some other content.
I have had about 90% of my traffic coming from stumble (about 5% from this site) for a total of about 5000 visitors in the 10 days it was open.
2000 of those visitors were because my
article about the US made so much controversy in the stumble community that it hit the popular section for Politics on SU. I got loads of good and bad reviews, it was interesting. I also gained about 10 fans.
So SU really does bring traffic to your site, but to get the most, you should have a good article. I find that controversy brings many visitors =)
Unfortunately, only one person clicked my ad :'(