I've been using the kit 17-85mm IS lens on the Canon 20D, and have just got a 70-300 IS DO lens. The IS is very easy to "feel" on the 70-300, as a sort of noise/ vibration as it works, especially at 300mm. I don't get any feel from the 17-85 at all from the IS, and I must admit I've found it very hard to see from the images whether it's working or not, whereas on the 70-300, turning on the IS makes a night and day difference.
Any thoughts on whether my 17-85 is functioning correctly??