Nikon S80 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Canon S90 has a
10.0MP 1/1.7-inch (7.44 x 5.58 mm ) sized CCD sensor and features Digic 4 processor.
Below you can see the S80 and S90 sensor size comparison.
As seen above, Canon S90 has a 1.5x Larger sensor area than Nikon S80. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.