SEOmoz | StumbleUpon - Demographics and Returning Traffic Spikes

Like most SEOs I know, I have a couple of sites that act as my side projects. They aren't monetised and I plan to keep them that way: I like to keep an eye on it for the purpose of experiments. By this I mean that I like to mess around with them and if one of them drops completely from every search engine, loses all of its PageRank and its server catches fire, it doesn't matter all that much....

www.seomoz.org/blog/stumbleupon-demographics-and-returning-traffic-spikes