MMO's like World of Warcraft have grown so much that old cities and areas in the game have been abandoned. They're still there though waiting for players to explore them.
Now a new hobby is popping up in MMO's of gaming archeology where players go to these forgotten areas to see what they can find. Old vendors selling rare items, skill masters, or simply old game designs. Its growing in popularity with each new expansion causing gamers to get nostalgic.