Failed to create Scene object. Compositing disabledThe solution was to turn off Xinerama and switch to using TwinView. I can't say that I'm thrilled with that, but since I only have two monitors on one video card at the moment, it does work.
Oh, and I'm learning to like the yum-skip-broken plugin... It makes yum a fair bit slower than usual, but a slow (but working) "yum --skip-broken update" is better than a failed "yum update".