At the past Ubuntu Developer Summit it was decided not to ship the Nouveau Gallium3D driver by default due to the aforementioned reasons, even though Fedora (among other distributions) are beginning to ship this driver so NVIDIA customers can have a capable open-source driver with 3D acceleration whether it be used by a compositing window manager or for gaming and other tasks. Nouveau 3D may still be quite slow in relation to NVIDIA's proprietary driver, but it isn't too slow for desktop compositing and lightweight gaming (with ioquake3-era games). Using a recent Linux kernel and Mesa release (circa Mesa 7.9+ and Linux 2.6.35+) this driver is also quite stable, we have not seen it render anything really wrong or produce artifacts, nor have any other problems been encountered. It may not yet support the very recent NVIDIA GPUs, but the Nouveau Gallium3D experience is quite good especially with GeForce 6 through GeForce 9 series graphics processors.
Canonical is now reconsidering whether to enable this driver in their Ubuntu 11.04 stock installation based upon Unity, the new desktop for Ubuntu. With Unity, Compiz is required as its window manager otherwise Ubuntu will fall-back to providing a classic GNOME desktop. Canonical sure would like to have Unity running on as many desktops as possible and by ignoring all Ubuntu users with the open-source NVIDIA driver would void it of being seen in many places, until NVIDIA's proprietary driver is installed.
As a result, Canonical now seems to be contemplating whether to enable the Nouveau Gallium3D Mesa driver so their Unity desktop can be used, especially from the Ubuntu LiveCD. As an alternative to enabling the Nouveau Gallium3D driver, another option they are exploring is making it easier to use NVIDIA's proprietary driver from a LiveCD. To accomplish running the binary driver from an Ubuntu Desktop LiveCD, however, that would require being able to uncleanly load the Nouveau DRM/KMS kernel module, build the Nouveau kernel module, and then load in NVIDIA's blob. The Nouveau option is a much better choice, but again Canonical is uncomfortable with Nouveau being "unsupported" and they don't want to invest in working on this community, reverse-engineered driver.
This work is talked about by Canonical's Christopher James Halse Rogers on Ubuntu-X. Canonical still has their plans to deploy Wayland eventually with the Unity Desktop and for that they will need kernel mode-setting with 3D acceleration, etc. Nouveau provides this where as NVIDIA has no plans to support Wayland right now. As a result, Bryce Harrington has already responded signaling a greater interest in getting the Nouveau Mesa driver working rather than investing in a way to get NVIDIA's binary driver to work more easily and cleanly off a LiveCD.
Let's hope Nouveau Gallium3D is turned on by default in Ubuntu 11.04, which will be released next April. Doing so will not only help users of the Unity desktop, but also those running GNOME 3.0 with the GNOME Shell and KDE users with KWin or once Plasma begins using more OpenGL.