Blizzard has made the official announcement that it's releasing patch 4.0.1 for World of Warcraft during the game's maintenance tomorrow morning. This is basically the expansion patch for the biggest MMO in the world -- even though World of Warcraft: Cataclysm doesn't arrive in stores until December 7, this patch will bring many of the mechanics and system changes to the game that players have been awaiting, including a huge amount of class changes and updates, a revamp to the glyph system and a new system of reforging items to change their stats. This patch will also include the recently announced guild changes and lots of other updates and tweaks to ready the world for the game's third expansion.

You may not actually be one of World of Warcraft's 12 million players any more, but even if you're not, we thought we'd give you a heads up. Patch 4.0.1 is the reason all your friends will be back playing the game later on this week.