I've had a Canon G9 for several days, and have been very pleased with the clarity of the lens, and the pixel-level sharpness. I decided to actually do a comparison today.
For background, the cameras are a 1Ds (classic!), with the 24-70 2.8L, and 70-200 2.8L IS, and the G9 with it's all-in-one 35-200 2.8-4.5 zoom (35mm equiv.).
Both cameras were shot in RAW. The G9's files were converted with Adobe's DNG converter, and then files were processed in ACR for PS CS2.
The 1Ds uses the color calibration tab, while the G9 did not. There was no sharpening applied in either ACR or PS. White balance, brightness, contrast, and curves were set on the G9 to approximate the look of the 1Ds.
Note that light levels were changing from shot to shot, and all images were shot hand-held. It was cold, so this is not an excruciating test.
I also did NOT match DOF, but chose to shoot in manual mode, to try to match light levels.
What I found:
Image quality: Surprisingly close, within the limits described below.
There are two huge differences between the two cameras. Focus on the G9 is slower, and you can't tell exactly when the exposure starts and ends. This really annoys me.
Also, Canon has really pumped up the exposure, and appears to be doing some funky things in DIGIC. RAW data seems to be overexposed, and then a curve applied that brings the midtones and shadows back down. Even shooting at EV -1/3 to -1, skies are easily blown.
Surprisingly, strong shadows in outdoor shots do NOT suffer from noise.
Here's some pics: (Remeber to click on the 'all sizes' icon for 100% crops)
http://www.flickr.com/photos/8927203@N02/sets