It is 6" vs. 5". The competitor for the Nook is the 650.
The Nook:
Weight: 7.48 ounces
Height: 6.5 inches
Width: 5.0 inches
Depth: 0.47 inches
The Sony PRS-650:
Weight: 7.58 oz
Height: 6.61 inches
Width: 4.68 inches
Depth: 0.38 inches
The Sony PRS- 350:
Weight: 5.47 oz
Heigth: 5.71 inches
Width: 4.11 inches
Depth: 0.33 inches