Nice find, especially the IS tests. As I suspected, but didn't want to burst any bubbles, you still won't be able to shoot at very long SS. Even on say the 24-105 I've found about 1/6 to 1/4s is the limit at 24mm, where as you get a full 4 stops IS at longer FL.
Once you get down to below these levels it is almost like being on a tripod as far as how steady you have to hold the camera and IS still moves the image around, just slowly.
But as a landscaper I'd still rather have IS than f2.8 and I strongly suspect an f2.8 lens of this quality without IS would be heavier.