Linus noted in his message that around 40% of the changes for this new test release are for the DRM code, largely to do with the ATI Radeon driver as well as the Nouveau driver for NVIDIA hardware that recently went mainline. There is also a moderately-sized update to the Intel DRM too.
This DRM work has fixes and such for EDID, the recently completed ATI Embedded DisplayPort for KMS, ATI SidePort memory detection for IGPs, TV load detection for some NVIDIA NV40 series chips, tiling support for NVIDIA pre-G80 ASICs, and many other changes all across the board. With the ATI Radeon KMS and Nouveau DRM still in the staging area, Linus was a bit more tolerable about accepting some of these changes late into the Linux 2.6.33 kernel development cycle rather than having to wait around for the Linux 2.6.34 kernel.
Aside from the heavy DRM updates, Linux 2.6.33-rc4 carries updates to other drivers, file-systems, networking, and the usual other patches.
The performance of the Linux 2.6.33 kernel continues to be tracked on a daily basis by us via Phoromatic Tracker at kernel-tracker.phoromatic.com.