Similar story to GlenP's, and the user was in a pretty rotten mood when I turned up.
I reckoned that the monitor needed a good, sharp knock to fix the wobbles, and the user was in need of a good laugh.
"The Power of Chris compels you !" *light tap*
"The Power of Chris compels you !!" *not-so-light tap*
"THE POWER OF CHRIS COMPELS YOU !!!" *whack*
The picture's now steady as a rock, and the user's laughing like crazy.
Sometimes, you have to fix the wetware as well as the hardware and software...