My brother in law recently purchased a Canon S90, and I was interested to see how the current state of the art in higher end compact cameras compared to my GF1. The S90 has some great features, and I would argue it is easier to use than my GF1... I've felt that the GF1 has significantly more satisfying results on screen at 100%. I do a lot of my work on screen, and sell stock so the pixel level does matter for that. In actual prints I would be happy with the S90 for most things. I did a quick shot in the yard today to compare then on a bright sunny day which puts the S90 in its best light (pun intended). Since I do a lot of work with the GF1 at low ISO for stock, it is only fair to compare it to the S90 at that setting.
I used to have a Canon G10, and often felt that areas in photos were mushy. Something like blades of grass or tree limbs would look great, but faces, singles on a roof or moderately busy areas didn't quite have the detail I can get out of a DSLR. I felt the same way looking at the S90. Looks great on review, nice prints, great for computer viewing, etc. - but lacking a bit at 100%. Below is a crop midway to the border of an image. Not a strict test, to be sure, but it shows what I consistently find when editing photos later. Just a bit mushier - look at the bench texture. Keep in mind that the GF1 is almost 3 times the price, and double the volume. I'd be very happy with the S90 if I didn't do stock. Note that the lens on my GF1 is the excellent 20mm prime compared to the S90's zoom. There is no doubt that the GF1 suits my needs well, and was worth the extra dollars to me. For my brother in law? The S90 fits the bill nicely too. Everybody's happy :)
Please don't take this comparison to the nth degree - the key here is that this is representative of results that I get with my camera... I wouldn't notice the difference in a 5x7 print done at a lab with these two cameras. Note the sensor size difference made me use a more open aperture on the S90 to avoid diffraction... Both are stopped down somewhat from their maximum apertures.