Don't know if it's a general problem, but I'm waiting for my N900 precisely because of that - the only reseller in town that sells the N900 had only one left and it had 4 nasty dead pixels (2 always on, 1 always off, 1 dead green subpixel) so I'm waiting for the next shipment...

As for your case, if it's just stuck (but not dead) pixel/subpixel, a gentle massage over it might help, or you can try with a small utility I wrote long time ago @ http://www.topflashers.com/etc/screenfix/ - it will give the screen a run for its money. Now I don't know how well Flash behaves on N900 (although it's pretty lightweight), does the fullscreen work, nor could it reach screen redraw rate of the N900, but it can do wonders for stuck pixels on desktop monitors. Of course, if the pixel/subpixel is dead, there is no help...

Cheers...