another hint for those experimenting with ubuntu:

you don't need an extra sd for that! uboot is capable of doing netboots. but that afaik doesn't work with the uboot from the repos. you may try however(uboot in general is capable of this !).

there is a different approach that also works. that is nfsmount. instead of using the sd as the rootpartition you mount the nfs via kernel nfs support. and chroot and pivotroot into that nfsshare. that way you boot into a directory on you pc, laptop whatever. but you have to setup a connection first. wlan is woking so no big deal, you only need everything necessary for that in the initrd.

with that testing gets realy comfortable. you edit all the files on your pc and immidiately see the effect on the phone. no further sd, no wearing off of sd's, cross compiling on the pc ...
hth

the usual edit: you can boot into nfs without initrd. the initrd is only necessary to setup the wlan.