For now only the Radeon DRM uses this new TTM memory manager implementation, but once ready, so will the Nouveau kernel mode-setting code for NVIDIA hardware. VIA's DRM will likely end up using TTM in the long-run too plus potentially other vendors. In the Linux 2.6.31 kernel, the Radeon KMS driver is being tagged as a staging driver until it has undergone greater testing. In the Linux 2.6.32 kernel the new ATI Radeon code will likely be marked as stable (and hopefully greeted by R600/700 KMS support too!).
This new code will hopefully be pulled into Linus' kernel tree for Linux 2.6.31-rc1 within the next day or two. With a bit of luck, hopefully it will not be characterized as untested crap by Linus, like when Intel had initially pushed their GEM (Graphics Execution Manager) GPU memory management code into the Linux kernel last year.
The Radeon KMS / TTM pull request can be read on the DRI development list.