So basically, I've been reading several different articles, etc. on running Debian and/or Ubuntu on Android. I did this on my Eris and D1 in the past, and I figured that it would work even better on the Galaxy Nexus. Of course it does... Anyway, it can be run from a loop mounted image or a separate partition on most phones. However, for phones like this one with no sdcard slot, it makes sense to just do the image thing.
After building and rebuilding an image a few times, I decided to do what I normally do and turn those crazy linux commands into a script. It's not really all that complex or fancy, but it works and can be improved. I hope you find it helpful.
NOTE: This is really just the first step in getting Debian running on your phone. This will just create the image. You still have some work to do. There are other ways to do this, but I like having control of the initial image...
1/14/2012 - fixed some typos and added 'apt' as a default package (debootstrap did this by default, but apparently multistrap doesn't)
1/16/2012 - removed multistrap and went back to debootstrap for now
1/21/2012 - added a setup script to do the second stage and updates after booting into Debian on the phone, fixed extra package install code
1/22/2012 - updated variable code per swordrune10's suggestion
Currently requires Debian 6, but feel free to fix that for me.