Players who're able to log on after maintenance is over today will discover that the Operation Gnomeregan and Zalazane's Fall world events are now available! These are two of the introductory Cataclysm world events. Head to Kharanos in Dun Morogh or the Echo Isles in Durotar to take advantage of these limited-time experiences.
To start the Echo Isles quests, you want to talk to Vanira, who is right next to Voljin in the Sen'jin village in Durotar.
To start the Operation Gnomeregan quests, you want to talk to High Tinker Mekkatorque, who is located in the Tinker Town district of Ironforge.
These quests are counting towards the Loremaster achievement.
More information on the event: