gnome-terminal's transparency support works correctly normally.  However, if I
set my nautilus desktop background to be a plain colour rather than an image,
gnome-terminal starts using massive amounts of CPU and becomes highly
unresponsive (5-10 seconds between pressing a key and getting a response).

Clearly there is some kind of problem with the way g-t grabs a copy of the root
window behind it that only manifests itself when the background is a plain
colour rather than an image.

This bug was present in 2.4, and persists in 2.6.

This may be a dupe of #137162, not many details there.