In an analysis of thousands of submissions over a three week period on audience voting sites like Digg and Reddit the Wall Street Journal reports that one third of the stories that made it to Digg's home page were submitted by 30 users (out of 900,000 registered ones), and that one single person on Netscape, who goes by the online handle "STONER," was responsible for 13 percent of the top posts on that site.
Any social media site that relies on the contributions of its users will find a similar distribution curve, with a relatively small number of top contributors representing the bulk of submissions. For instance, user-submitted stock photography site iStockphoto has more than 35,000 contributing photographers, but only about 100 have sold more than 100,000 images (at about $1 to $5 a pop). The difference is that with iStockphoto, users submit work in hopes of getting paid. The financial incentives are very clear and upfront because it is an e-commerce site.
But with services like Digg or StumbleUpon which increasingly drive attention to other Websites, contributions are supposed to be driven by the heart, not the pocketbook. As a result, there is more of an incentive for marketers to try to influence the top users on those sites with outright bribes. That's why opportunist startups like User/Submitter are popping up to game these user-controlled sites by setting up payola schemes for marketers to siphon money to the top users to promote their products and services.
What Digg and every other social media site needs is a trustworthy reputation system, where top contributors can get paid if they choose but also must disclose who is paying them, and other users can then vote on how much they trust those people. Otherwise, these sites will eventually be filled with the equivalent of spam links. (Although, in Europe at least, such deception may come under new regulations which will bar companies from "falsely representing oneself as a consumer," depending on how strictly those rules are interpreted).