Nope, it's not the pad contrast Henry.
Even running it over a newspaper makes no difference. If the mouse suddenly gets it into its head to take off for a top or bottom screen border, that's it.
Not caused by spyware cutting in either (using S&D Spybot plus Adaware SE). Registry First Aid, System Mechanic 6, Registryfix and Registry Mechanic and PCMedik in use. Nothing makes any difference.
TS