I have two Ubuntu 7.10 systems that I tried upgrading to 8.04. The first (x86_64) encountered a bunch of problems during the Clean-Up phase, causing a whole slew of package system complaints on reboot, while the second (x86) failed during the Installing/Upgrading Packages stage, leaving my system in an “unusable state” and leaving me unable to start Gnome.

More details are on Launchpad: the first system were all semi-automatically reported tickets using the new error reporting system (which sets the tickets to be private), and one ticket for the second system.

Last time I tried upgrading was from 7.04 to 7.10 on my Dell Latitude D600, which also failed and brought my system into an “unusable state.”