hey,
firstly a quick question, does your screen wabble when you type? also does the screen close under gravity if you leave it 3-4 inches wide.? also check one more thing, close the lid and look from the side of the powerbook, does the lid seem to have shifted back?
if you see any of those then call apple up, i had the same problem my screen was too loose and it would wobble when i type fast and the screen would fall undergravity beyond some position and over time it had shited slightly back also leaving a lip in the front.
and apple went in and tightened the screen for me and changed the hinges.
hope that helps