I found another interesting site using the World of Warcraft Armory for some statistical data mining. This one is called WoWProgress. Besides tracking the progress of guilds in WoW, it also tracks movement between guilds in some charts. Did you for example know that priests switch guilds most often, but hunters switch least often. Interestingly while for every class it is more likely that somebody switches from a weaker guild to a stronger guild, priests seem to be the most burned out class, and are the class that most frequently moves from a stronger guild to a weaker guild.
WoWProgress also has another interesting feature: It tracks people who moved from one server to another or changed name. If you want to really disappear, you better change your gear, otherwise somebody with a specific set of gear leaving one server and somebody new appearing out of nowhere with the same gear is going to leave a trace.