I've had it and a friend with a g4 powerbook as well. I don't have applecare, but 'luckily' it happened within a year. Now I have a call number I can use when the problem returns and it will still fall within the first year guarantee.
I had a problem with my 12" 700combo iBook as well. On a Dutch forum for macosx more people had the same problem. (vertical lines on display when pressing the area left of the touchpad).
We all called applecare who were aware of the problem (production error I suppose) and applecare fixed...