If you asked me a few months ago, I probably would have never considered this lens, due to the combination of reason's already listed (size, weight, push-pull, price, etc.). It's biggest pro, is versatility.
However...
This summer I did have the opportunity to test one out on my 5D III, for about a half hour. I did like the lens, much more than I would have expected. Although, the image quality may suffer a bit, compared to some of Canon's other offerings, it was still quite good. If I could pick up one of these for under $1800, possibly refurbished, and the stars aligned, I might consider one.
Of course, I'm not sure what I would use it for. It's not fast enough for most of the action I shoot and it's too big for a walk around lens. I also have much better lenses for portraits and landscapes, so I guess it could keep my 100-400mm company, in the bag, since it also rarely gets used.