I absolutely love StumpleUpon's video recommendation plugin. I now get great video's to watch highly tailored to my taste. Here is a lecture I ran into by Luis Von Ahn, a CS professor at CMU, lecturing on his approach to developing clever and addictive games to leverage human computational power to solve important problems. For example, one of the games allows him to build a database of metatags for images on the web. He argues he can metatag effectively all image content in Google's image search with his user population in a very short period of time. This lecture left me thinking social networking sites are significantly under utilizing their user populations.