Comment 5 for bug 486361

Exactly the same situation: I had my workstation perfectly working with 9.04 AMD64 with all latest updates and did a Dist Upgrade from Upgrade Manager. The upgrade did not complete for some reasons logged into /var/.... could not do anything but restart the system.
At boot, the system could not mount any of the md devs I have, (0,1,2,3, respectively /, swap, /home, /stripe).
Could do nothing since the busybox recovery terminal was read only. Could see that the mds were ok using cat /proc/mdstat but could not assemble the arrays to boot the computer. So after reading the above I did:

1) fsck (maybe not needed - but found many errors)
2) manually mount devs rw with
sudo mount /dev/md0 -o remount,rw
sudo mount /dev/md2 -o remount,rw
sudo mount /dev/md3 -o remount,rw

Note: /dev/md1 is swap, already mounted rw

3) aptitude update -> could not run, so sudo dpkg --configure -a and apt dbase rebuilded
4) aptitude update
5) aptitude upgrade and restart after finish - OK!

But to do all this I had to have:
1) another computer available
2) pretty good system knowledge
3) cold blood

I can imagine the average user clicking "upgrade" and then have a non bootable system!

Ubuntu+RAID=not for fainted hearts

Rich, thank you so much for posting this info! You're the man...