World of Warcraft accounts that have not been accessed since 2008 and before will see the names reclaimed by Blizzard to free them up for other players to use. Those wishing to hold on to legacy account names will want to log into each character in order to preserve the name.
Our goal with this great name liberation is to make sure new and returning players have a large and varied pool of names available to choose from—so log in now if you wish to preserve your unused characters’ names for your journey intro Draenor.
Source: World of Warcraft Community Site