Comment 18 for bug 275451

I had the same issue on my daughters PC after upgrading from 8.04 to 8.10 then to 9.04. I did not test between upgrades so the fault may have started at 8.10.

During 1 of the upgrades it gave an option to use my custom dhcp.conf or a new one, I chose new.

On the first test after the final upgrade.
I found that none of the roaming profile accounts could login, unable to find /mnt/home/user
I then logged in with a local account and found that the NFS mount had not mounted. mount -a worked.

My solution was to backup /etc/network/interfaces then delete the originals.
Then in the NetworkManager Applet I setup a static IP.
rebooted, tested roaming accounts, now able to login.

Ram