but I wasn't expecting it to be so awfully SLOW (kicad has its own cursor that seems to lag the actual mouse movement by about half a second, as the main annoyance.)
I have to say I never experienced that (Ubuntu 9.10 32 bit), and I don't think that is a normal operation of it.
I briefly tested kicad in windows XP and ubuntu 10.4 64 bit too, also no lag there.
The track width selection was a mess as well.
That I can agree with. I would want quick a drop-down list of (user editable) predefined widths, instead of typing it in when I want to change it.
Undo function is not the best either as you say.