ComputerWorld has an interesting
article up about how the various flavors of Linux are working, or not working, towards running on the new Intel
Macs. Since the chips in the new Macs use the relatively new EFI (the successor to BIOS) most Linux distros will not
work on the Intel Macs, yet. Ubuntu, Novell, and Red Hat are all working on porting their OS's to the new Macs.
One flavor of Linux that you won't be able to run on your brand spanking new iMac (ever) is Yellow Dog. Terra Soft will not be porting their OS, which was designed especially for the Power PC architecture.