This is a really handy tip for wanting to keep your computer awake or keep grooveshark playing, using a cup.
Laser mice only...
I don't use this hack myself, my desk is glass and causes this effect anyway, plus the mouse wets itself if you don't use a mouse mat like the ever classy sheet of a4 paper.
Step 1: Put a Cup Upside Down...
Now balance the mouse so the sensor is hitting the corner of the cup.
When it's right the mouse will keep the bright LED for moving on instead of stopping after a few seconds.
Step 2: Or Break a Glass?
I broke a wineglass the other day, one of the pieces suits this purpose perfectly, though any lump of transparent material will do.