Well, that's mostly inside the GPU/DRM area. There are also ALSA improvements, support for thermal monitoring on recent AMD K10 chips, and various new drivers have also arrived.
Using the Linux 2.6.33 kernel we have already looked at the EXT4 file-system performance and also found some Btrfs performance improvements in Linux 2.6.33.
At the start of the Linux 2.6.33 kernel development cycle we also launched the Phoromatic Kernel Tracker where the latest Linux 2.6 Git code is being benchmarked on a daily basis with a whole assortment of tests. If you head on over to kernel-tracker.phoromatic.com you can see how the performance has evolved each step of the way during the development of the Linux 2.6.33 kernel.
The Phoromatic Kernel Tracker will continue going forward with the Linux 2.6.34 kernel and if you have visited the tracker page in the past few days you will have noticed more systems appearing (including daily benchmarks of Btrfs!) and other changes taking place. Those Phoromatic Tracker changes will be announced in the coming days as the 2.6.34 development gets underway, but there's even more exciting and useful information coming out of Phoromatic and the Phoronix Test Suite for this next kernel release. Stay tuned!
The Linux 2.6.33 kernel release announcement by Linus can be read at LKML.org.