I upgraded to ubuntu 11.04 yesterday and played my first KGS game with it today.
It's a clean install.
While playing it looked like the stone hitboxes got a lot smaller. I had to wander with my mouse around the place where I wanted to play in order to find where the foggy black stone would appear so that I was able to place it. (I eventually lost on time)
I don't know if this has already been reported or if this is related to KGS at all, tough it only happened there.