OK...I finally tested my 5D's image stabilization by taking some dimlit indoor pics, no flash, w/image stabilization both on and off. There is a significant differance. Let me just say it works well. Turned off all the pics were a bit blurry...Switched to "On" almost all were sharp. (Tested in auto & 1/8-1/30 sec. f5.6, depended on where I aimed.)