Previous blog post ended with a question: "if the AF is lost, how about the IS? How to find out?"
Many people say that you can hear the Image Stabilyzer in action as soon as the shutter button is half-pressed. Honestly, on the 18-55 IS lens, I didn't feel/hear anything. Other references online tend to confirm that the lens is "quiet" and you can't tell the IS is in action.
Another test is to shoot two pictures, with and without IS, freehand, and look at the difference. You need the proper subject and light too, and perhaps more than just a couple of shots (and maybe 10 coffees...).
Then it occurred to me once that if I hold the camera lens against my ear (grab the camera with the right hand, so the bottom side of the lens touches the right ear) and half-press the shutter button ... I can hear a faint ringing, like a few small bells at the other end of a tunnel. When the IS switch is turned off, no ringing can be heard.
What does this mean?
Well, in my case it means that probably the IS is still working despite the AF being out of order. If you have doubts, listen closely to your lens whispers.