Is It True That IS only helps by 1 f-stop? (1 f-stop = f/0.2) If Not, What Is?

IS or VR in the camera body only helps by about 2-3 stops, though I've also read that 1 f-stop number you quoted. IS or VR in the lens helps by 3 to 4. I just know that I can handhold my Nikon 18-200mm VR at 1/4 second with excellent results.

Here's a quote for Popular Photography. Look carefully at the chart on the rightside of page #2..
"So far, lens-based IS has the lead, with one Nikon VR lens logging a 3- to 4-stop improvement (a few big tele zooms barely reached 2 stops). In contrast, the best result from a sensor-shift DSLR is 2 to 3 stops, with the average closer to 2 stops. "
http://www.popphoto.com/cameras/4615/image-stabilization-special-stop-the-shake-lab-report-page2.html

usually up to 3 stops
it depends on the camera

Thank you George. :-)

Most lens-based IS is good for at least 2-3 stops, but don't think of that as an f-stop improvement. Think of it as a shutter speed improvement. You are able to use a lower shutter speed, but the f-stops available to you will obviously be no different than they are without "IS."

Tom Tom is correct.

You are wrong. A full (one) stop is f2 to f2.8 to f4 or 1/125 to 1/60 to 1/30 or 1/125 to 1/250 to 1/500 - at a constant ISO.

how does IS have anything to do with stop?