If you are lucky enough to have a store with K10D/K20D in stock, ask to see live view on the demo unit, with a longer zoom.
Turn on liveview and leave SR off, shake the camera, like really shake it.
Then turn on SR and shake it the same.
Watch the difference on the screen.
I suggest this only since you can't see anything in the viewfinder due to in body IS, if you pick up a Canon IS lens and watch the IS engage, you know it works and how well it works.
Using live view to get the same warm fuzzies i think is appropriate.
Expect the same real world results as with newer generation Canon IS lenses, just expect it on any lens, new or old, expect it even on a $90 500mm f/8 mirror lens