Back when Google was doing it's beta test program for Chrome Netbook, I applied and luckily received my own free CR48 laptop.
I have used Chrome OS for a while and while it's pretty good if you just always want to use chrome browser I was feeling a bit lonely without root access and gnome desktop. So I manned (nerded) up and flashed CR48 BIOS to allow running unsigned code and installed Backtrack 5 on it. Now CR48 is infinitely more usable and entertaining. All hardware (except 3g modem, I haven't gotten around to using that yet) works fine, and I didn't have to install any drivers manually. Only thing I had to do is create a non root user for use for desktop type tasks because by default Backtrack only has root user.
Here are the steps that you can follow yourself to install any OS compiled for x86 on your CR48:
Back up then flash CR48 BIOS
This step is necessary to allow booting of non-signed images. I followed directions on this page: http://corey.degrandchamp.com/2011/04/10/flash-google-cr-48-bios-without-luigi-or-ubuntu/ with much success.
I had some trouble opening up CR48 and I had to use a small metal lever to force the case to come off. Make sure to not apply too much force lest you break something. But also don't expect the case to come off too easily.
Make bootable USB or SD card
If your BIOS is succesfully flashed you should be able to insert a bootable USB or SD card and boot from it. This way you can install any OS you like as long as it is made for x86. I haven't tried 64 bit versions yet, but they should work.
I used Unetbootin to make bootable USB for Backtrack, and had pretty easy time installing it on my CR48. Grub2 worked fine and I can dual boot back into Chrome OS pretty easily at start up.
I used gparted to resize STATE partition (make it smaller), and install a new bootable partition right before it on which I put Backtrack. You could just erase chrome OS as well, but I am not sure how easy it is to recover to factory state if you do this. (probably not too difficult using Chrome Recovery USB: http://www.google.com/support/chromeos/bin/answer.py?answer=1046510).
Originally this article talked about installing Linux Mint, but I changed it to Backtrack 5 because that is what I ultimately ended up using on my CR48. Mint does not seem to be a good choice for netbooks.