ubuntu-bug really, really seems to want me to ask this as a question on askbuntu.com rather than reporting it as a bug. So I am.
My machine (for which ubuntu-bug has not attached any details for you, but two salient details are that it's an nv graphics card and 2 x 1920 x 1200 heads) takes roughly a half second to change window focus when I move the mouse to a new window. This is very long, enough that I have to think to wait. A reasonable goal in human interface design would be under a tenth of a second.
It's worth noting that I am using sloppy focus mode (focus follows mouse-enter events).
I'm not quite sure how to phrase this as a question, unless the question is "what's the right way to report this as a bug?" or maybe "any suggestions how to tune compiz, and how can we make it so ubuntu users don't have to tune compiz?".