This switching though from TTM to GEM though has caused a few problems (some technical and some political) within the X.Org community. Two examples are X.Org 7.4 losing DRI2 support due to a rework being required over TTM-specific bits and a a new 2D X acceleration architecture based upon EXA but designed to implement GEM.
This memory manager has only been in development for a few months, and Intel has been preparing to merge GEM to master since June, but today they have finally achieved this goal. Two days ago Intel's Eric Anholt had merged the GEM changes to the mainline xf86-video-intel 2D/DDX driver and today he has merged the Intel Mesa 3D component. The Mesa changes consist of changing the Intel i915 driver to using the GEM interfaces for object management.
These GEM-powered components will officially in xf86-video-intel 2.5.0, which will officially ship later this year, and on the 3D side the version will be Mesa 7.1. This Mesa update is due out soon as it's holding up the release of X.Org 7.4 and X Server 1.5.