It seems you don't shoot video. Shooting at 1/30, 1/60 or 1/4000 does not improve eliminate shake in video, but IS cuts it down quite a bit.
Hand-held video is common even on big budget films today. Eliminating the micro-shakes improves the look quite a lot. The camera on a shoulder brace with a 50mm with IS is great on FF, and even more important on a crop.
No, I shoot lots of video. My point was that IS for video and IS for stills is entirely different because of the contiguous nature of video footage. Most photo lens IS has been designed for photo use, i.e. short bursts of agressive and noisy IS, not prolonged smooth and quiet IS.
It seems you didn't read the second part of my answer. Supported. Could be a studio pedastol. Could be a shoulder rig. Both of which would negate IS.
IS for video is called steadicam. And it works on the entire set up, not just one part of it. I'm not saying that in lens IS can't be used for video, just that it sucks.
Can you tell me one film that you can hand on heart say has been shot with an unsupported 'hand held' camera, that is no rig, no steadicam.
Perhaps think smaller than a film coming from a huge production house (i.e. a wedding film, student film, etc.). IS definitely helps those run and gun shooters. IS even helps if your glidecam operator isn't the most adept....
And I hate to return to the IS debate, but...
So far, just about everyone arguing for IS on this 50mm f/1.8 cite being able to shoot at a smaller aperture (f/4, f/5.6) in low light. And that's because if you're shooting at f/1.8 you can get away with 1/50, 1/60 for just about anything, especially with ISO performance these days. I think many of these people would be far better suited by the 24-105 IS or by Tamron's 24-70 f/2.8 VC (IS) than by this lens. It has yet to be argued that someone needs IS while shooting at f/1.8...and honestly, I can't think of any photography situation where I'd need/use/like IS at f/1.8. Like I said earlier, I can shoot at 1.8 & 1/50th of second for everything. If I want a wider DOF I have much more versatile IS zooms for that. If I want to get creative with motion/light, I'm going longer than just 1/13 on my shutter. Sure, shooting at 1/13 would give me less noise than 1/50th, but I'd be more restricted in what I could shoot. Plus, noise reduction is free.
Consequently, this just screams video lens to me. If I'm filming a wedding reception I'm going to be wide open, and IS will definitely help during those moments where I'm clumsy/not as steady, etc. (by the reception I've already been filming for ~8 hours).