[beholder3]

M.L.E. It does this only in video, or also with stills?

There is no difference between video and stills with image stabilised lenses in general. So that is what you see with stills as well.
So much about the "general" "advantage" of SR in lenses. It simply depends on which lens exactly you are talking about.

[Dan Rentea]

I've rented on Saturday a Sigma Contemporary 150-600mm lens (for Canon) and I saw a little flickering in the viewfinder when I zoomed at 600mm (IS was turn on). Except this minor inconvenience, I can say that the stabilisation works pretty well at 600mm with long shutter speed (1/80s, 1/100s or 1/125s). I have to do more testing, but after the first 800-850 shots taken with this lens, I think it's worth the money.