When upgrading Ubuntu (Oneiric Ocelot) 11.10 to (Precise Pangolin) 12.04 DO NOT reboot using kexec; this will lead to slowdown, lag, choppy video, keyboard and mouse movement. Do a complete shutdown -hP now shutdown and cold-boot when the upgrade program tells you to reboot.

Software versions: Kubuntu 11.10 i386 with the KDE 4.8 PPA's, upgrading with console do-release-upgrade -d