In terms of performance, although the SX1 IS is supposed to be the high-performance model of the two, the SX10 is by no means slow. It starts up in two seconds and shuts down again in about one and a half, which is very fast for a super-zoom camera. In single-shot mode it has a shot-to-shot cycle time of 1.8 seconds, while in the standard continuous shooting mode it can snap away at 0.7 seconds per frame, apparently until the memory card is full, which is certainly above average. There is also an AF continuous mode, although this is somewhat slower.
The autofocus system is a bit of a departure for Canon, since this is the first model in ages that doesn't have the much criticised multi-zone AiAF system. Instead it has a simple one-zone AF mode, with a dedicated button to quickly move and resize the AF point. In practice this is exactly how most people were using previous Canon models anyway, so they've simply omitted a feature that nobody was using. The simpler system is quicker, easier to use and most importantly a lot more accurate.
I found exposure metering to be accurate and reliable, although in very high contrast situations it did tend to over-expose somewhat, burning out some bright highlights. Dynamic range is actually quite good, so it is better than most at preserving shadow detail. The SX10 has Canon's iContrast function for boosting shadow detail, and it does work very well, with hardly any extra noise.
The overall image quality is very good. The lens has fantastic centre sharpness, and the level of recorded detail is superb, among the best I've seen. Wide angle barrel distortion is kept to an acceptable minimum, and telephoto pincushion distortion is also thankfully mostly absent. There is some chromatic aberration toward the edges of the frame at al focal lengths, but again it's kept to an acceptable minimum.
Despite the smaller 1/2.3-inch sensor, noise control is also very good. While noise is visible from 200 ISO upwards, Canon's usual process of reducing chroma noise more than luminance noise means that images at 400 and 800 ISO still have plenty of fine detail and good contrast. 1600 ISo is a bit of a mess, but not totally unusable.
The PowerShot SX10 IS is an expensive and quite complex camera, and not really suited for the beginner, however in capable hands it is capable of producing excellent results, and has enough creative versatility to do so in a wide range of situations. Build quality, handling, performance and image quality are all up to Canon's usual high standard.