In Fedora 12, you can install mesa-dri-drivers-experimental package to get the experimental 3D support for a number of ATI chipsets and in Fedora 13, this package will have 3D support for Nvidia via the Nouveau driver.
In my Fedora 13 development system, I have
# rpm -ql mesa-dri-drivers-experimental
While there is still work to be done including performance and power management, enormous progress has been made in the last six to eight months and I think by oct, we would be in a state where we can run GNOME Shell out of the box for the large majority of modern desktops. I think, there is a fall back option for users who prefer running the older GNOME panel as well.