I installed Fluxbox, killed Xorg and logged in again. I got a usable desktop, rather than a blank white screen. Progress, sort of. I brought up Gnome's configuration editor, and told it to use metacity, not compiz, logged out, and back in. No change. Checking, however, it's still using compiz, not metacity, and metacity is known to be installed. Weird! However, this does point to Gnome and/or compiz as being the culprit.
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