On our Dell Inspiron 8200s we set them to not suspend when the lid is
closed.  This is done through the BIOS.  On WinXP this is also usually
an option in the Power control panel, so I must admit I had assumed most
machines had the option in some form or another.  Certainly the 8200
draws most of the air in at the side and vents at the back.

Having the machines configured this way means we can leave them running
overnight or during a compile.  I always close the lid when I'm not
using it as the screen backlight turns off (and in my painful experience
this is usually one of the first components to wear out in a laptop, so
anything I can do to extend the life of the machine I will).

"Simply" disabling a sensor seems silly to me, you would lose this
display conservation advantage.  But at the same time it would be
extremely annoying if my machine suspended when I put it on one side
(with the lid closed to stop a pet walking on the keyboard ;).
__
David B.