Back in October there was the very controversial news that Canonical would be replacing the GNOME Shell with their own Unity project
as the default desktop shell for Ubuntu 11.04 and going forward. The original version and specification for Ubuntu Unity (and as found in Ubuntu 10.10 Netbook) required 3D acceleration and would use Compiz as its compositing window manager. For those without the necessary graphics drivers to support the functionality, Canonical's plan for Ubuntu was to have it fall-back to the traditional GNOME desktop and inform the user of their sad graphics support. However, now Canonical's developing a 2D version of Unity for such scenarios.
The "Unity 2D" desktop is to provide a Unity environment without the need for OpenGL or any accelerated graphics drivers, but is built using Qt and QML. The goal is to have Unity 2D to have a close to the same look and feel as the normal Unity environment. Canonical found a need to provide this Unity 2D option especially with many mobile ARM-based platforms lacking the needed OpenGL drivers, or at least for being available "out of the box" since nearly all of the ARM graphics drivers are poorly-supported binary blobs.
Unity and Unity 2D will be found in Ubuntu 11.04, to be released this April. There's also a Launchpad page
for this new Unity 2D project.
Hopefully this move to provide a non-OpenGL Unity experience will not diminish the chances of seeing the Nouveau Gallium3D driver in Ubuntu 11.04