Canon G11 has a 10.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor and features Digic 4 processor. On the other hand, Canon G10 has a 15.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor .
Canon G10's sensor provides 5MP more than Canon G11's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the G11 and G10 sensor size comparison.
Canon G11 and Canon G10 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Canon G11 has 46% larger pixel area compared to Canon G10, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
DxOMark Sensor Scores
Both Canon G11 and Canon G10 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, G11 has scored 47, 10 points higher than G10.