Lead Encounter Designer Daelo has posted over on the forums that the testing of Icecrown for patch 3.3 will begin tomorrow, October 15th, with the Lord Marrowgar encounter. Blizzard will also have the trash before him up and working as well -- the Icecrown raid preview describes the fight as an army of undead guards, commanded by Marrowgar, "a monstrosity fused together from the bones of the undead." Sounds like good times to us.
Stay tuned -- we'll definitely have a few players available to test the encounter and give you some impressions from the PTR tomorrow, and if we can get enough folks together, we might even stream it again. As Daelo points out, the testing schedule will be extremely flexible, so Blizzard will likely pull bosses up and down at a moment's notice -- they've got a lot to test and probably less time to do it than they'd want. Note also that this is for US PTR servers only -- the EU will have a seperate testing schedule that will be available on their forums when it's ready. To Icecrown!
Patch 3.3 is the last major patch of Wrath of the Lich King. With the new Icecrown Citadel 5-man dungeons and 10/25-man raid arriving soon, patch 3.3 will deal the final blow to the Arthas. WoW.com's Guide to Patch 3.3 will keep you updated with all the latest patch news.