As we've discussed in several articles over the months, a lot of webmasters have been going overboard with link removal requests in the wake of Google's Penguin update and link warning emails. People are trying to get links removed that they shouldn't be - links that very likely are not hurting them in Google. It's essentially the SEO equivalent of killing a bug with a rocket launcher.
Danny Sullivan posted an article today about how StumbleUpon is even getting these kinds of requests. Given the amount of traffic StumbleUpon can send to websites itself, completely independent of Google, it's hard to express how ridiculous this is.
StumbleUpon confirmed with us that they do indeed get these messages from webmasters. The company tells WebProNews, "We typically receive a few of these requests a week. We evaluate the links based on quality and if they don't meet our user experience criteria we take them down. Since we drive a lot of traffic to sites all over the Web, we encourage all publishers to keep and add quality links to StumbleUpon. Our community votes on the content they like and don't like so the best content is stumbled and shared more often while the less popular content is naturally seen less frequently."
As Sullivan says, "StumbleUpon to remove your link is a waste of time. I’d say. That’s the type of link you actually do want."
If Google has a problem with links you're getting from StumbleUpon (which it seems unlikely that they would), you're probably better off with the StumbleUpon referrals anyway. That said, you shouldn't be spamming StumbleUpon, and should be creating quality content that SU users would enjoy (and there are a ton of very niche categories). StumbleUpon won't hesitate to ban you if you're abusing its service.