By my calculations, the pixels are not quite square on the 5"and 8" versions:
Code:
5" 600x800 185x194 ppi
6" 600x800 168x166 ppi
8" 768x1024 152x158 ppi
9.7" 825x1200 147x148 ppi
For comparison, the typical UMPC color LCD screen has about 133 pixels per inch, although the new Samsung Q1U has 170 ppi on a 7"screen and the Nokia 700/N800 has about 225 ppi on a 4.1" screen.