display randomly wakes up

[scar]

i am using ubuntu 10.04 on a desktop computer and having a strange issue
where the LCD display is randomly waking up.  for example, i go AFK and
then my power-saving settings go into effect, putting the LCD to sleep.
 then, at random times, it seems, i will notice the LCD is not sleeping.
 sometimes it wakes me up at night.  the screensaver is still running,
though.  i don't think the mouse is getting moved inadvertently.  is
there perhaps something running on the system that could cause this?