Tried to upgrade to the Ubuntu 9.04 Beta today. Upgrade itself went smooth, restart didn't, seems like Nautilus ran amok opening a gazillion windows, currently worked around by killing and removing Nautilus. Might not be Nautilus fault, as there is something fishy with the gnome-session manager.
Button mapping for my mouse and Wacom got mixed up as well, that was fixed by a simple:
xinput set-button-map "Wacom Intuos2 6x8" 3 9 1
xinput set-button-map "ImExPS/2 Logitech Explorer Mouse" 3 2 1 2 2 2 2 2 2
The eraser on the Wacom still doesn't work.
Gimp and Emacs don't start from the panel, even so their command line seems correct. A new icon drag&dropped from the Application menu works, maybe some incompatibilty in the .destkop file or so?
Krita4 still crashes on startup.
Flash doesn't work even so the flashplugin-nonfree is installed. Seems to work now after creating a new Profile.