Intel's Graphics Execution Manager is a kernel memory manager for graphics processors and has since overtaken TTM in what will become the de facto standard for GPU memory management. A technical explanation of GEM can be found here.
Intel has been working on merging GEM to master since June and then in early August it was finally merged into xf86-video-intel for the Intel driver's memory management needs. The GEM kernel component is still missing from the mainline Linux kernel. During XDS 2008 in September it was stated that GEM should be ready for the Linux 2.6.28 kernel and that was confirmed again today as being ready for the next kernel release.
Due to the timing of GEM's introduction, DRI2 was dropped from the X Server 1.5 / X.Org 7.4 release due to its dependence on Tungsten's memory manager (though for X Server 1.6 it has been corrected).
GEM had also caused the introduction of a new 2D acceleration architecture for X that has been called UXA, or UMA Acceleration Architecture. Intel's Keith Packard though has clarified that UXA will eventually die off with the GEM-related bits being moved back into the EXA architecture.
Intel's Jesse Barnes has published a new blog post talking about GEM for Linux 2.6.28 and other related topics. Jesse confirms that everything is still on track for being pushed into the Linux kernel once the 2.6.28 merge window is open. The kernel mode-setting bits will be merged too. Additionally, Jesse stated the xf86-video-intel 2.5 release is still coming along and should be out soon. As a result of the Intel e1000e networking troubles, he's also made a few PCI improvements that improve safety.