The optical image stabilization system used on the SX1 IS works in the same way as all the current range of Canon compact cameras. There are three modes: Continuous (IS on all the time), 'Shoot only' (IS is activated at the moment the exposure is made) and Panning (for horizontally panned shots).
The first option makes framing easier - the IS system steadies the preview image, but we found that the shot only option produced more consistently sharp images at the extremes (where the shutter speed is more than 3 stops slower than would normally be used for the focal length you're shooting at). Shoot only - which doesn't steady the preview image, is more efficient because it minimizes the amount of corrective movement required by waiting until the instant the picture is taken.
The design of the SX1 IS makes for very steady shooting - especially when using the EVF - which is evident in the IS off results. The SX1 IS is able to produce sharp results at 3 stops under the 1/focal length rule without IS, and adds another stop with IS turned on. As long as you take a few 'safety' shots, the body design and IS system will allow you to produce sharp results at shutter speeds where subject movement will be more of a problem then camera shake. This is a good thing since the relatively slow (aperture wise) lens will require you to use shower shutter speeds quite often in everyday situations.
The stabilization test
In this simplified version of our SLR IS test, four hand-held shots were taken of a static scene with the stabilization off and on. The shutter speed was decreased and repeated (from 1/1000 sec to 1/8 sec). The zoom was set to a position between widest and most telephoto (200mm equiv.), the test target was 6 m away from the camera. The test was repeated three times and an average taken.
The resulting images were then inspected and given a blur score - 'Sharp' (no visible blurring at 100%), 'Mild Blur' (the kind of camera shake that is tolerable at small print sizes) and 'Heavy Blur' (virtually unusable due to camera shake) and 'Very Heavy Blur' (little discernible detail).
The results below show that Canon's IS system gives a impressive two stop advantage, which is improved on the previous IS system used in the S5 IS. This is important to make the larger zoom range and higher resolution of the SX1 IS just as usable as the S5 IS.
Hand-held, no stabilization (200mm equiv.)
As you can see from the chart below that the steady body design of the SX1 IS allowed a majority of results to be sharp at 1/30th (3 stops below what would normally be required) with IS turned off. With some safety shots, even 1/15 sec is usable.
Hand-held, IS Continuous (200mm equiv.)
With IS turned to continuous we produced all sharp results at 1/15th sec, and 1/8th is usable if you take a few extra images.
Hand-held, IS Shot only (200mm equiv.)
Setting IS to shot only produced slightly better results than continuous. We managed to get a majority of sharp results with the shutter speed set to 1/8th sec, which is 5 stops slower then what you would normally expect with IS off. We even managed to get some sharp results at 1/2 sec, which is a setting that you can only use to shoot stationary subjects.