- Size and weight: thinner, with fewer angles and odd protrusions, so it's more likely to fit in your pocket.
- LCD: brighter, and seems slightly larger when shooting in 4:3 mode (due to wider format of LX3's LCD).
- Controls: control rings are not perfect but allow for quicker, more intuitive settings adjustment compared to the LX3's joystick. I especially like the control wheel on the back of the S90, even though some have complained that the wheel is too loose, I never found this to be a problem.
- Low light performance: I had much better luck getting properly exposed photos in low light with the S90, although you do have to keep an eye on the ISO as it doesn't take much to introduce a fair amount of noise. The S90 does apply a fair bit of noise reduction to low light shots, so although noise is not as noticeable as the LX3, the S90 has reduced detail. I didn't test either camera with noise reduction software (e.g. Noise Ninja). Even at higher ISO settings, I had trouble getting the LX3 to take a usable photo of a street at night lit only by streetlight, while the S90 picked up on it right away in aperture priority mode.
- Lens cap: the S90 has none. Instead it uses automatic shutters to protect the lens. The LX3's manual lens cap is a minor annoyance, but an annoyance nonetheless (one more thing to lose).
- Lens: 24mm versus the S90's 28mm provides a wider and more useful field of view for architectural or landscape shots, although there is a lack of sharpness at the edges if you look closely.
- Daylight performance: the LX3 has the edge here due to the S90's tendency towards chromatic aberration (purple fringing around high contrast areas, which is the same problem my 5 year old Powershot S410 has - not sure why Canon hasn't fixed this yet).
- Aspect ratio: LX3 offers 4:3, 16:9, and 3:2 (my preference is for 3:2) shooting modes without cropping or changing the field of view. The S90 allows you to shoot in the same ratios, but does this by cropping the 4:3 image, which is just throwing away image data.
- Video: neither camera will satisfy a video enthusiast, but the Lx3's 720p video is the standard these days. There's no reason the S90 had to be hamstrung by VGA resolution (640x480) video, as HD video has been featured on much cheaper cameras for a while.
- Flash: I don't like the tendency of the S90's flash to automatically pop up where you're holding the camera. The LX3's pop-up flash has a switch to release it - much better.
- Build quality: The LX3 feels solid. The S90 doesn't feel flimsy, but lacks the LX3's fit and finish.
- Image stabilization: I got usable shots down to 1/2 second exposures, but not reliably from either camera. IS is definitely helpful but not a miracle.
Conclusion: Both cameras are excellent. However, I didn't find that either one represented a quantum leap forward versus my old Canon Powershot S410, not enough to justify +$400. So a Nikon D90 DSLR (or possibly the new micro four thirds Panasonic GF-1) is my next stop. And it's really a shame that Canon couldn't make the S90 clearly superior versus the LX3 given that they've had a entire year to refine their product.