The culprit may be be (from /var/log/dpkg.log):
2008-11-21 20:31:01 install nvidia-glx-96 <none> 96.43.09-0ubuntu1
Doing System / Administration / Hardware Drivers and then disabling the nvidia driver -- and then rebooting! -- seems to make the problem go away on my compaq r3000.
The culprit may be be (from /var/log/dpkg.log):
2008-11-21 20:31:01 install nvidia-glx-96 <none> 96.43.09-0ubuntu1
Doing System / Administration / Hardware Drivers
and then disabling the nvidia driver -- and then rebooting! --
seems to make the problem go away on my compaq r3000.