Being an owner of the lens (Nikon fit) I can say that mine does auto-focus throughout its range and from a lot of reviews I read there isn't a lens of this type that could compare to the sharpness you'd get from a set of prime lenses... but the whole point of an all-in-one like this is the convenience, I decided to get one for this reason and will be getting other lenses for other occasions - they all have their own role.
I have a Nikon 55-200 (not relevant for yourself I know) and I think it can produce a bit sharper images but I wanted an all in one for general walk-abouts and the images it has given so-far are fine. I am going for a walk with it tomorrow it give it a bit more of a trial.
HTH, if you want any specific info etc. let me know.
Ian