To tell the truth, I am a bit disappointed from the IS of this camera. I was hopig that it will do a better job.
The S5's IS is among the the the most effective among P&S cameras. It does not, however cure all causes image blur such as subject motion or focusing errors. Below is a quote from DPReviews IS tests:
"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). I wouldn't read too much into the fact that our results for the relative effectiveness of the two modes are the opposite to what we saw with the S2 IS; 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.
I certainly found it made handheld shots at 3, 4 or even 5 shutter speeds slower than normal perfectly possible. Impressive stuff (though the reliability is much better if you're within 3 stops), and if you take a couple of 'safety' shots when pushing the system hard (1/30th at 432mm for example), you'll usually get at least one 'keeper'. "
The full comments can be found at: http://www.dpreview.com/reviews/canons5is/page6.asp
Good technique still counts. Use the EVF rather than the LCD as the camera will be steadier up against your face rather than away from your body. Use two hands with the left hand under the camera. The camera will be steadier if you're sitting or kneeling and circumstances permit. If there is a handy wall or column, lean against it. I shot an auto show last Saturday with my Kodak Z612 (IS) and 90% of my shots had shutter speeds of 1/8-1/10 sec., almost all of those I was kneeling, both for composition reasons and for steadiness, and all but about three where sharp. I do grant that I'm 13 yrs younger than you.
It might be useful if you could post a few of your pics and let the group examine them to see if camera shake is issue or something else is going on. Be sure the EXIF data is attached.