I saw a reference to this still fairly new site WoWProgress earlier reading over at Tobold's blog. Its another one of those sites that provides lots of WoW guild ranking, tracking, player statistical data of the various sorts from WoW Armory data.
You can also find armory information information on character gear pieces and when they got it or statistical data on guild raiding loot. However seems you can do some detective work as well on players recruited where you recruited them from and if they left where they went to in various degree. It also seems to be able to somehow track players that use the Blizz witness protection program and change their name as well or switch servers in the process which can get interesting if you do that line of work. Anyway just another tool if you need to find info you may be looking for.