Game Update 54, "Will of a Tyrant," is now on the Test servers.  It contains Frostfell and a plethora of bugfixes!  See our Game Update 54 page for complete test notes.

Kiara posted on the official forums:

Shaders won't be going in with this update.  They are still analyzing and tweaking performance.

The update is in fact GU 54, we're calling it Will of a Tyrant - the update is the massive bug stomping.  Also in this update, but not necessarily immediately activated on test when it updates later today - Frostfell and the second part of the prelude events leading up to the expansion. 

Game Update 54 is expected to go live on December 1, 2009.