OK, I did a *very* quick and dirty test. Cameras were the E-1 + 50mm f/2 macro lens, and the 5D + 100mm f/2.8 macro lens. In theory the Oly 50mm is equivalent to the Canon in size of image based on sensor size. The shots were converted in Silkypix using default RAW settings, and then converted in Photoshop, no adjustment on the original image apart from unsharp mask of 300% at 0.3 for the Canon and 250% at 0.3 for the Oly (my default sharpening). Normally I would do a lot more adjustments to levels and contrast so don't judge the image quality on these shots - I'm just trying to show the differences in detail.
I won't tell you which is which, but it should be quite clear (oh, and apologies for the subject matter - he's a wizened old owl when it comes to dad taking yet more shots
).
image 1
crop 1
image 2
crop 2
The difference in detail is quite significant I think, and I've found this is consistent with all shots I've taken with the two systems (the lighting wasn't very good on these, which has meant less detail than I would normally expect). When printing however (at least up to A4), a lot of this detail is less obvious from normal viewing distances - which I guess is answering Mr. P's initial question.
The other thing that I've found consistent is the quite radical differences in colour, particularly in skin tones. It's obviously a personal preference, and it can all be altered in post, but I do prefer the warmth from the Oly in this area (though I often tone it down just a touch).
btw - the settings for these were:
Canon: 1/60sec @ f/3.5 ISO 200
Oly: 1/160sec @ f/3.2 ISO 200