The Intel driver integrating their Graphics Execution Manager as a kernel-driven memory manager and replacement for TTM is a major milestone. GEM was introduced in May after open-source developers became concerned with TTM, the memory manager developed by Tungsten Graphics that was set to become the de facto standard for graphics memory management. A key advantage that GEM has over TTM is that it's simpler to develop for, but developers working on non-Intel drivers have had to use a mix of TTM and GEM to accomplish their graphics memory management needs. The kernel bits to GEM had entered the Linux 2.6.28 kernel just last week. Those building the xf86-video-intel driver on a Linux 2.6.28 development kernel or newer will be able to use GEM while older kernels will be without this support.
As a result of GEM, the Intel driver has a new 2D acceleration architecture. The UXA Acceleration Architecture was introduced in August after Keith Packard took EXA and began replacing it with pieces of GEM code. Keith hopes to merge his UXA work back into EXA for the X Server 1.6 release later this year, but for now it's living independently as UXA. UXA is only designed around Intel UMA hardware and is present in this 2.5 release when GEM support is available. Proposed this summer was dropping XAA acceleration support from the Intel driver, but that was postponed from this release.
Unlike GEM, kernel-based mode-setting support has yet to enter the mainline Linux kernel (it will likely be merged in Linux 2.6.29). The Intel 2.5 driver though is compatible with building against a KMS-supported kernel. One requirement of this new Intel driver though is libdrm 2.4.0 or later.
Intel had hoped to fix the video tearing issues with Textured Video / XvMC by version 2.5.0 of this driver, but that goal wasn't met. As DRI2 though has been fixed with GEM support after this memory manager caused its delay from X.Org 7.4, expect improved video playback in the near future.
Intel's xf86-video-intel 2.5.0 release announcement can be read on the X.Org mailing list along with the source driver package.