So I got my lens last night and had a change to fire off some test images. WOW, this thing is HUGE. None of the photos I've seen do it justice, even on my 22" monitor
To to settle the debate: hand holding the lens is POSSIBLE in the most desperate of situations, or when IQ just isn't a priority. Shake reduction works like a charm with this thing though, and is not to be underestimated. The reason this lens can't be hand on a regular bases held is simple: The focus ring is too far back to be a point of support for the lens, so when you are supporting with your left hand just in front of the tripod mount, you're holding the camera with your right hand so you can see in the viewfinder. You must then take your right hand off the camera (putting all th weight on your left) focus with that hand while trying to maintain vision in the viewfinder, then move the right hand back to the camera to steady and shoot. Admittedly this problem would be somewhat rectified with a shoulder mount...it might be possible with that.
Anyway...I will be using this lens a LOT, whatever support I end up with.
On to the sample images. Don't bother pixel peeping, they're not that sharp, but if I were stuck without a support and some rare bird jumps into frame, it can be captured and displayed very successfully at web sizes or small prints, I have no doubt. These shots were late in the evening with the light fading, so shutter speeds were lot, iso was 200+ and aperture was wide open or one stop down. Caveat: I have fully processed and sharpened these images, so this isn't some resolution test, nor does it show what the lens is capable of.
1/500, ISO200, ~f5.6, braced on my knee. Focus point is on the dude.
1/125, ISO400, f4.5, again braced on my knee
1/200, ISO200, handheld. Not too sharp, added noise, lots of processing
1/250, ISO400, handheld. Nice portrait lens!