Letting the upgrade run in the background doesn't quite work. There are just one or two steps that want some interactive confirmation, interspersed with a lot that don't. I seem to recall a similar problem on the initial install, too.
Annoyances so far:
(1) My Chrome icon on the taskbar thingy ("panel"?) became nonfunctional. Worse, I could not remove it because it was so nonfunctional that right-click didn't work. And all the documentation I could find about where the taskbar state existed didn't match my setup. It turned out to be .gconf/apps/panel/objects/object_0. Documentation suggests this should be in "unity" instead? Who knows.
(2) I have two network adapters in this computer. One of them is no longer plugged in, causing periodic pop-ups alerting me to this fact. I found some very helpful documentation explaining exactly where to go in gconf-editor to disable this behavior. It didn't work. Workaround: disable the configuration of that port. Which I'm sure will cause me a headache later.
(3) I really did not need an orange-themed desktop.
On the plus side, memory usage seems to have actually decreased!
mark@erdos:~$ cat /proc/swaps Filename Type Size Used Priority /dev/sda5 partition 4881404 184 -1 /dev/sdb5 partition 4881404 0 -2
On 10.04 a half-day of running the web browser would easily have pushed 200-300MB to disk.