MMO Champion and Wowhead have each put two and two together and worked out the possible release date of World of Warcraft: Cataclysm. They reckon it will December 7th.
Their logic goes like this: Zarhym, a Blizzard employee, mentioned in an off-hand announcement about the current arena season that the next season would begin about a week after Cataclysm's launch. Then, buried in a snippet of game text, it seems like both Wowhead and MMO Champion found this:
"Arena battles and Rated Battlegrounds are only available during an active player versus player combat season. Season nine will begin on December 14th, so be prepared at that time to take your shot at glory!"
One week before December 14th? December 7th. Additionally, it looks like Blizzard has hidden this date in cryptic, totally-not-obvious quest text - a Goblin engineer states that the chance of any sort of worldwide Cataclysm occuring is "less than 12.7%". As Wowhead say, "Looks like we have a release date of December 7th on our hands. Tentative, of course, don't quote us, but there you go."