StumbleUpon has been in the news recently due to its recent aquisition by eBay. StumbleUpon is a social bookmarking network consisting of over 3 million users or stumblers each of whom use the StumbleUpon toolbar to find and review web pages, viral videos, online photographs and more. The StumbleUpon algorithm then learns what the user likes and then let's you channel surf the Internet to recommend and display to the stumbler similar sites.