Well, the Ubuntu team really screwed the pooch on the latest upgrade. I manage three Ubuntu machines, all with clean installs of 9.04. Well, I locally upgraded one of them, and tried to remotely upgrade the other two.
For the local upgrade I used the GUI, and for the remote systems I used do-release-upgrade as instructed.
All three upgrades failed, in various ways.
The local upgrade lost its internet connection. I had to MANUALLY select the Wired Connection 1 after upgrade.
The two remote ones failed (I had to visit the machines) on reboot, failing to mount the file system.
Then one (perhaps two) of the remote systems did an interface swap, rendering them inaccessible on the internet.
It seems this particular upgrade was not tested sufficiently prior to release, as any google search on this upgrade will show.
This was the Vista of Ubuntu upgrades for me and many others. A complete disaster, and likely to throw beginners off of Ubuntu and linux for a long time.
I was buried in command line hell for hours to get this upgrade to finish, and needed a friend to fix the network problem introduced in this release.