From WOWInsider: If you remember from yesterday, various developers and CMs posted across the official WoW forums that Season 4 will be mostly ending on the day patch 3.0.2 is released. Today, Nethaera posted some additional information: Season 4 will end on October 14th. It was not explicitly stated by Nethaera that patch 3.0.2 will be that day, but two plus two equals four, you know?
This is pretty much exactly in line with the date most of us have been guessing here at WoW Insider, but let's be honest. It wasn't hard to figure out, and I'm sure all of you guys were thinking much the same thing. It'll be almost exactly one month between patch 3.0.2 and the release of Wrath of the Lich King on November 13th. It will also be after BlizzCon and not before it, so if anything goes wrong their lead devs can jump right back into work instead of needing to worry about the convention.