StumbleUpon, founded in 2001, was one of the first sites to become wildly popular by helping people find amusing, weird, and useful things on the internet. Bored at work? Idle at home? By repeatedly clicking StumbleUpon’s simple "stumble" button, it’s possible to scan through hundreds of websites in one sitting, as its algorithm takes stabs at what you might like. Here’s a recipe for pasta pie. Here’s a video of a robot walking up some stairs. Here’s Anderson Cooper’s blog. It’s mindless, and it's brilliant.

According to StatCounter, StumbleUpon drove more traffic in 2009 than any other social media site in the US, including Facebook, YouTube, Twitter, Digg, Reddit, and Pinterest. But like other content discovery sites, StumbleUpon is having trouble turning diversion into a business — especially now that traffic has plummeted following a big redesign.