I just upgraded the Kubuntu Hoary Hedgehog partition on my iBook to Breezy Badger. I left it a while to allow any obvious problems with the new release to be ironed out. What a breeze it proved to be:
$ sudo sed s/hoary/breezy/g -i /etc/apt/sources.list
$ sudo apt-get update
$ sudo apt-get dist-upgrade
Then it took about 36 minutes to download the 500-odd Megs of required files over my 2 Mbps line and about another 20 or 30 minutes to perform the upgrade. During this time, it asked me three questions: permission to stop some services, what default language to use, and whether to replace the global Xsessions file.
Everything looked fine. Everything still seemed to be working. A reboot resulted in a nice new login screen and no odd behaviour. Logging-in took me to my familiar desktop. Touch wood, but it all seems to have Just Worked. Very impressive.