Landing into the Linux 2.6.37 kernel DRM was initial mode-setting support for GeForce 400/500 "Fermi" graphics cards, but it went without any actual acceleration support. With the Linux 2.6.38 kernel there is now initial open-source acceleration support for NVIDIA Fermi GPUs, so the DDX driver bits have now been merged into the mainline xf86-video-nouveau display driver.
The NVC0 merge done by Red Hat's Ben Skeggs plays with about 5,000 lines of code and allows 2D EXA acceleration to work as well as X-Video video playback. The big git commit can be found via FreeDesktop.org CGit.
One of the other exceptions to the Nouveau Fermi support is that it currently requires firmware not living within the mainline Linux kernel tree to operate. Nevertheless, the GeForce 400/500 series open-source support is moving along without the support of NVIDIA.