Speaking to a small conglomerate of various Alliance representatives, Mekkatorque pointed out that the time to strike is now. After all, Thermaplugg has eluded death for years to keep his reign over Gnomeregan; and with the fall of the Lich King, the last great threat to the citizens of Azeroth, the chance of any cataclysmic event taking place in the foreseeable future is "less than 12.7%," Mekkatorque's leading combat medical advisor Doc Cogspin purported.

12.7

12-7

So it's either November 30th or December 7th, thanks to the wonderful achievement:

+ARENA_MASTER_NO_SEASON_TEXT = "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!";

and this wonderful post:
zarhym wrote:The next Arena Season will begin for level-85 players approximately one week after the official launch of World of Warcraft: Cataclysm.

Thanks for the release date Blizzard!

Edit:

I had my crystal ball out, all I'm sayin.

IRVINE, Calif., Oct 04, 2010 (BUSINESS WIRE) — Blizzard Entertainment, Inc. today announced that World of Warcraft®: Cataclysm™, the highly anticipated third expansion for the world's most popular subscription-based massively multiplayer online role-playing game*, will be released starting on December 7, 2010. The expansion will be available on DVD-ROM for Windows® XP/Windows Vista®/Windows® 7 and Macintosh® at a suggested retail price of $39.99 and will also be offered as a digital download from the Blizzard Store. A special Collector's Edition packed with bonus items will be available exclusively in retail stores for a suggested retail price of $79.99.