Yup, I'm seeing this, with 'Focus follows mouse' on -- which I vastly prefer compared to having to click the window to in order to click in the game (two clicks if it is unfocused, one click of it is focused == bad juju).

Had no luck finding the part of the Control Panel metioned in the previous post in this thread.

I did turn off the taskbar's 'always on top' and that at least keeps it hidden wihle it is flashing it's yellow/orange 'OMG your wow window changed' notification. And the keyclone 'always on top' combined with 'focus follows mouse' will keep the taskbar buried during play. I'll try a session with it set like this to see how it goes. Happens on both Vista and Win7 for me, btw.