The optical image stabilization system used on the G9 works pretty well for most everyday photography - though don't expect miracles. 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, and we found it more consistently effective at extremes (where the shutter speed is more than 3 stops slower than would normally be used for the focal length you're shooting at) than the shoot only mode.
Shoot only - which doesn't steady the preview image, but is theoretically more efficient because it minimizes the amount of corrective movement required by waiting until the instant the picture is taken - is perfectly effective when you're nearer to the correct shutter speed (and once you're within 1 or 2 stops it is actually more reliable). You may find you get different results than me; we have no quantitative tests for stabilization, and every person's 'shake' is different; users often disagree on which mode works best, so you just have to find which best suits your style of shooting.
Overall I was very impressed with the G9's system, though the design of the G7 means it is more prone to camera shake than some of its larger 'SLR-like' competitors, such as the Panasonic FZ50.
These tests are rather extreme - up to four stops slower than you could safely use without IS - and in 'real life' shots - where you are maybe using a shutter speed two stops slower than normal - the system is remarkably effective- as long as you support the camera carefully with two hands and don't try to 'grab' shots too quickly.
The stabilization test
In this simplified version of our SLR IS test, ten hand-held shots were taken of a static scene with the stabilization off and on. The shutter speed was decreased and repeated (from 1/200 sec to 1/13 sec). The zoom was set to its maximum position (210mm equiv.), the test target was 3 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).
As the charts below show the IS system does give you about a three stop advantage over shooting without IS, and even dropping down to four stops below the recommended minimum for a 210mm lens I was getting usable shots half the time, with one in four perfectly sharp. Impressive stuff.
Hand-held, no stabilization (210mm equiv.)
As you can see from the chart below even at 1/200th second I was unable to get more than half the shots I took at 1/200 second completely sharp (this is probably due to the design of the G9, which is built for style over comfort). By the time you get to 1/50th sec (2 stops down from the recommended minimum) it's almost impossible to get a sharp - or even usable - result.
Hand-held, stabilization on (210mm equiv.)
With stabilization on the results are much better - we got no blurred shots at all above 1/200th sec, and the majority of shots down to 1/25 sec have little or no blur. Even down to 1/13 sec - a good four stops below the recommended minimum - you've still got a 50:50 chance of getting something usable, and if you take a few 'safety shots' you'll get at least one completely sharp.