You often hear about how different Facebook and MySpace’s user bases are. Well, maybe they’re not so distinct after all. Yahoo is the No. 1 traffic referrer to both sites. (Hat tip to the purple team). What’s more interesting is how much traffic they actually send to each other: Facebook is the second-highest traffic source to MySpace, and MySpace is the third-highest traffic driver to Facebook. The other sites they get the most traffic from are portals (guess portals aren’t exactly “dead”) like AOL, MSN and, of course, Google. As for the app developers, it’s worth noting that Zynga and RockYou are two of the top sources of traffic to both nets.