Performance is always a Canon strong suit, and the IXUS 100 IS is no exception. It starts up very quickly in just over a second, and shuts down again in just over two seconds. In single shot mode it has a shot-to-shot cycle time of 2.2 seconds, which is good but not exceptional, while in continuous shooting mode it can maintain one frame a second, which is also about average for a modern compact camera.
The autofocus system also appears to be the same as the IXUS 110 and 990, with a choice of either face-detection and tracking in AiAF mode, or simple centre-point AF with two zone sizes. The AF is nice and quick, but I've seen quicker, including the Casio EX-S12. As usual the AiAF system works very well, apart from occasionally when it decides to focus on some random element in the background of a scene rather than the largest or closest subject.
As you might expect from a camera pretty much purpose-built for social snapshot photography, low light performance is excellent. The AF is just as fast in low light, and thanks to a good AF assist lamp it will work in total darkness at a range of several metres. The flash is also surprisingly powerful for its size, easily surpassing its stated maximum range of 3.5 metres.
Image quality is of a very high standard, although not without its faults. Noise control is good, but no better than most other premium 12MP cameras. It produces good image quality at 400 ISO and usable pictures at 800 ISO. Canon has sensibly capped the maximum sensitivity at 1600 ISO rather than including a useless 3200 ISO setting for the sake of it as many manufacturers do.
The only real problem with image quality is a persistent tendency to over-expose by about half a stop, which unfortunately tend to result in rather washed-out colours. Dynamic range is also a bit limited, although the intelligent contrast control helps to preserve some shadow detail.
The Canon IXUS 100 IS is almost a novelty now, a 3x zoom ultra-compact when all around are wide-angle long-zooms. It's a nice looking camera with excellent build quality and a good range of features. Performance is good, especially in low light, and the image quality is also generally very good. However the awkward handling and almost pointless tiny viewfinder limit its appeal.