The traffic posted by someone else above seems unrealistic at best to me since I got all of <100 unique visitors out of the deal. I assumed he was going to stumble one url from 30 different accounts but his English blows so I wasn't sure. For $4, it didn't really matter though. I imagine it will at the very least have slight SEO benefits.
it is not about english it is about your understanding.
stumble doesnot allow one site that is stumbled once to submit it again.That is why i use your site pages to stumble it for 30 times.
i use different accounts and stumble on by one page of your same website.
This gives variety and also trick the stumbleupon.
i hope you get the idea now.
30 accounts = 30 pages of the url(website)
thnx