I have a similar problem to this. I'm running Ubuntu 7.10.
When I have it on for a while the screen flips and makes the computer unuseable, but if I go to the shutdown screen the display comes back. If I'm editing photos or doing something processor intensive, then it can be about an hour before the screen messes up.
I'm currently looking at ACPI support, hoping that the temp sensors need to be recalibrated, but i'm having no luck at the minute...