What's exciting us in particular about the Linux 2.6.39 release is another round of graphics driver updates. The Linux 2.6.39 kernel DRM has the open-source AMD Radeon HD 6900 "Cayman" GPU support, the Nouveau driver for reverse-engineered NVIDIA support now has KMS page-flipping and Z-compression, support for USB DRM drivers, TTM kernel memory management support under Xen, and various other fixes and improvements to the various Direct Rendering Manager drivers.
The Linux 2.6.39 kernel also presents a basic Poulsbo KMS driver, but without any acceleration support at this time.
Outside of the DRM-land, there's support for USB 3.0 hubs, virtualization improvements, and other fun.
The official release announcement by Linus Torvalds for the Linux 2.6.39 kernel can be read at LKML.org.
While this is an exciting bleeding-edge release, the two regressions we've been talking about lately are still very much outstanding with this release: the Linux kernel is still burning through power and Intel Sandy Bridge support broke at the last minute.
Meanwhile we can go get excited for the Linux 2.6.40 kernel. We've already been talking about the Linux 2.6.40 kernel a fair amount on Phoronix, but its merge window is only opening up today obviously with 2.6.39 out the door. The 2.6.40 merge window will be slightly shorter this time around due to LinuxCon Japan coming up.