Achievement system spotted in Wrath of the Lich King
According to this Death Knight post, an Achievement system in the World of Warcraft Wrath of the Lich King Alpha test can be accessed by typing in "/achievement".
There are some screens of it over there, showing awards for things like "total death", general PvP and exploration.
The WoW update is planned to release at the end of this year and will be shown at the Blizzard Worldwide Invitational at the end of this month.