The update apparently trashed the xorg.conf file. "sudo dpkg-reconfigure -phigh xserver-xorg" seems to fix it.
It seems that while I was flailing around in 640x480 mode, I deleted part of my control panel. Does anybody know how to get back to the default panel? I tried to add a main menu, but that just puts up an icon whose drop down contains Places, System, Applications, etc. I used to have those in individual tabs on the main panel. I'd like to get the default look back, as I got sort of use to it. It's no disaster if I can't.
Thanks for the pointers, Scott.