I ran a script that installed Ubuntu on my Chromebook (Cr-48 ), saw that it did and then went back to Chrome OS. The link I used (plus follow ups) can be found here: Easy way to install Ubuntu on the Cr-48
The other method requires Flashing the BIOS and then like a regular computer it can have anything installed.
I would read through the Chrome OS Lounge because I think there are some steps to take for getting the special nav keys (there is no F1, F2...) and the extra-large touch pad working.
News here http://ubuntuforums.org/showthread.php?p=7546011.