The Nouveau kernel mode-setting support is still very experimental as their API isn't even finalized and it will not enter the mainline Linux kernel in time for Fedora 11. Red Hat though will patch the Linux 2.6.29 kernel to introduce this Nouveau KMS support for those who wish to use it instead of the DDX mode-setting within the X Server. The nouveau.modeset=1 string will need to be added to GRUB in order to enable kernel mode-setting on NVIDIA hardware using this community open-source driver in Fedora 11. By Fedora 12, hopefully we will see the Nouveau KMS support enter the mainline kernel, but that still would be cutting it close. This feature proposal can be found on the Fedora Wiki.
Enabled by default on Fedora 11 will be Intel kernel mode-setting (along with the ATI kernel mode-setting that can already be found in Fedora 10). More on this is also available from the Fedora Wiki. ATI kernel mode-setting has been enabled since Fedora 10, but in Leonidas the support will be extended to support KMS on ATI R100/200 hardware.
Kernel mode-setting allows for a nice, flicker-free boot process with the Plymouth project, fast VT switching, improved suspend and resume support, and other benefits. Kernel mode-setting is also a prerequisite for running the Wayland Display Server.
Ubuntu will not be enabling any kernel mode-setting bits until the Ubuntu 9.10 release, the Karmic Koala. Intel kernel mode-setting support entered the mainline Linux kernel with version 2.6.29, but the forthcoming 9.04 release is shipping with Linux 2.6.28. In time for Ubuntu 9.10 we will hopefully see some level of ATI kernel mode-setting support enter the mainline tree. Ubuntu 9.10 is also set to replace USplash with Plymouth.