Crash on mouse move after updates

[Colin Law]

After updates today my 11.10 laptop is misbehaving badly (though I
cannot be certain it was the updates as I was experimenting switching
between unity and unity-2d and plugging and unplugging external
monitors so it is possible something I did there triggered it).  On
the login screen if I move or click the mouse or touchpad lightdm (if
that is what it is) appears to crash, the text display appears for a
few seconds and then the logon screen is redrawn.  If I logon without
touching the mouse then everything is fine until I touch the mouse
when again it crashes and goes back to the logon screen.

I have tried
sudo apt-get update && sudo apt-get dist-upgrade
sudo apt-get install -f
sudo dpkg --configure -a
but none of these indicated that they had done anything.

I have a dual boot on the machine and am able to boot into 12.04 with
no problems so hardware can be ruled out.  All I see in syslog at the
time of the crash (from the login screen) is

Feb  3 21:05:04 piglet acpid: client 1060[0:0] has disconnected
Feb  3 21:05:04 piglet acpid: client connected from 2323[0:0]
Feb  3 21:05:04 piglet acpid: 1 client rule loaded

Note that as it happens from the login screen it would not seem that
it is anything to do with unity.

I have no idea what to do next so any suggestions will be much appreciated.

Colin