xkcd, one of my favorite geeky web comics, posted their second proportionate map of online communities: Online Communities 2. It represents the relative amount of social activity of various sites and programs as the size of fictional countries on a map. I wasn't surprised that Facebook is so huge, but I had no idea that FarmVille was that large, or LinkedIn so small.
Below is the map from October 6, 2010, and below that, the first Online Communities comic from 2007. Click the maps for higher resolution versions.
The 2007 original: