For our favorite part, the DRM / graphics side, the Linux 2.6.39 kernel provides Radeon HD 6900 series support, enabling tiling support for R600+ ASICs, the Nouveau driver has the aforementioned KMS page-flipping and z-compression, there's initial support for USB GPU DRM support for eventually having a DisplayLink DRM driver, TTM memory management support with Xen Dom0, and various other 2.6.39 DRM changes.
Within the kernel's staging area is also an Intel GMA 500 Poulsbo driver that has basic kernel mode-setting and TTM support, but it goes without any acceleration support and is quite rudimentary for now.
In this cycle, Linus once again criticzed the DRM code development with there being a number of fundamental issues.
Besides the graphics excitement, there's various new drivers, and many updated hardware drivers. In the Linux 2.6.39-rc1 release announcement, Linus notes there are a number of ARM updates, further VFS clean-up, and a new block device plugging model.
The Linux 2.6.39 kernel is shaping up to be a modest release although users relying upon their distribution vendors packages for their kernel will not be finding this in any of the major H1'2011 releases (e.g. Ubuntu 11.04 and Fedora 15 are using Linux 2.6.38), but will be waiting for the major distribution roll-outs in the second half of this year where they will be shipping with the 2.6.39 (or 2.6.40/2.6.41) kernels.