1st Ubuntu was ported to the Nook Color and now hackers at the XDA Developers have overclocked it to run at speeds up to 1GHz. The custom kernel ups the speed of the CPU while running it at a lower voltage, which means longer battery life. The system became unstable at the 1GHz level, but there were no problems at 950MHz. The code is at XDA. Go try it out.
Now when the Kindle comes out with color it should be interesting to see what hacks come out for it. Until then there is no point to get a Kindle if you can do so much with that Nook Color.