Where the 990 IS begins to really shine is its overall performance. It starts up in comfortably less than two seconds and shuts down again even more quickly. In single shot mode it can maintain a shot-to-shot time of approximately 1.8 seconds, while in continuous shooting mode it can maintain just over one frame a second.
Partly this performance is due to the excellent autofocus system, which is quick enough in good light to reliably capture fast-moving subjects, and can track detected faces. In low light it is unfortunately less reliable, and despite the extremely bright AF assist lamp it has trouble focusing even on nearby subjects. However in this situation the camera appears to default to a pan-focus setting that will at least get most of the frame looking sharp.
The overall image quality is very good, as one might expect from such an expensive camera. The lens provides excellent sharpness with only a little blurring and a touch of chromatic aberration at the very corners of the frame, and wide-angle optical distortion is kept to a good minimum. Image noise is particularly well handled, with very good image quality at 400 ISO, although quality does drop off dramatically at 800 and the maximum 1600 ISO settings, particularly in lower light levels.
The level of detail is exceptionally good, and the compression rate is nice and low at around 10:1. The only real problem with the image quality is, as I mentioned earlier, a bizarre tendency to turn all Caucasian skin bright lobster pink when shooting in Auto mode, both in daylight and when using the flash. It is possible to avoid this by using the My Colours option in Program mode, but for anyone who relies on the Auto mode it's obviously going to be a disadvantage.
The Canon IXUS 990 IS is undeniably a very good camera. The build quality is above any reproach, the handling and performance are excellent, and the range of advanced features is as good as anything else on the market. The optical image stabilisation is particularly effective. However it is very expensive even when compared to its few direct competitors and it is not without a few minor faults, particularly low-light focusing and unnatural skin tones.