Here’s my first set of comparisons between the Canon S90 and the Olympus E-620, both photos taken at the full frame equivalent focal length of 28mm.
The S90 raw file was converted using DPP, and for the E620 raw file I used the Adobe DNG converter and Photoshop CS3.
Both photos have the shadows lifted a bit, and then have the “Smart Sharpen” filter applied with a 0.6 pix radius and strength of 198%, using Remove Lens Blur and the “More Accurate” checkbox checked.
You can make your own judgments. My opinion is that in the center of the frame, there is absolutely no resolution advantage for the E-620 despite its sensor having an extra two megapixels. However, the E-620 crops appear slightly better because they have better contrast and colors. The corners are another story. The E-620 is far superior in the upper right corner (bottommost comparison) where the S90 image is quite soft. Unfortunately the upper right corners don’t match because they weren’t framed identically, and there isn't much fine detail observable in either corner so you may find it hard to judge.
14-54mm @ 14mm ("28mm")
f/5.6, ISO 200, 1/800
f/4.0, ISO 80, 1/500