I just bought one.
I've only had it a day, but here are a few things I've noticed:
1. The closest camera I can compare its noise profile to is the SD790 IS...which I also own. Images can get a little too "processed" at high ISO, but are otherwise acceptable for a high-res camera with a tiny sensor. SLR-like? Hardly. But do you expect that in a camera like this?
2. Unusually sharp across the frame for such a broad focal range, more so than the S2's lens was. But there's
noticeable barrel distortion at full wide angle.
3. Chromatic aberration is noticed, but it isn't really intrusive except at wide angle and F2.8 (wide open). At smaller apertures, CA is virtually eliminated.
4. The ultrasonic motor is fast, smooth and quiet. When the camera focuses, you hear some minor noise from the lens but it's nothing serious.
5. AF speed is speedy at wide angle, a bit slower at telephoto, but either way...it's an improvement over the S2 IS I once owned.
I haven't had it long enough to really get used to it, but I thought I'd share those tidbits.