I've heard that the quality of sharpness is improving in newer zoom lenses, but another downfall is with many variable focal length lenses comes a variable aperture versus a fixed aperture. Pain in the butt!
Some zooms have fixed apertures. I have an 80-200 2.8... but they tend to be $$$ because it isn't exactly a multipurpose consumer lens; more special purpose, like sports/nature photography.

~Tiff
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"Were the diver to think upon the jaws of the shark, he would never lay hands on the precious pearl."