When minimizing windows (I'm assuming) Metacity grabs the X server to draw
the window resize animation. Unfortunately this the undrawn state of the
windows behind it in for the duration of the animation. This looks rather
ugly, and some people find it very disconcerting (I personally hadn't
noticed this, but two people have now commented on the problem to me after
using GNOME 2 for the first time).

I have no idea if this is soluable within X. Could we maybe use a shaped
window for the animation instead of grabbing the x-server, or something? I
really have no idea what's possible and what's not. Perhaps if having a
window with a transparent hole in it (i.e. what the current animation does)
isn't possible, we could do something ala MacOS/X and have an image of the
window at the point that resize is clicked moving toward the tasklist and
scaling. This might be cooler too, and would allow a window to be used
rather than snagging the X server.