Recent upgrade causes sluggishness when changing workspaces

[Brandon Kuczenski <brandon 301south net>]

I recently upgraded to Gnome 2.12 and to Xorg from XFree86.  Now when I 
use keyboard commands to change amongst my four workspaces I get a 
noticeable (and aggravating) delay of about a second before the 
newly-selected workplace finishes rendering.  The only way I've managed to 
get the problem to go away is by selecting "no wallpaper"-- it seems to be 
present whenever I have any wallpaper selected.

I'm absolutely sure this problem just appeared because I find the machine 
almost unusable in its current state (I switch workplaces quite often). 
Any idea how I could go about troubleshooting this one?

Thanks in advance,
Brandon