I've had my 18-200 VRI since my D80 days in 2007 and has served my well on all adventures and now resides on my D7000. After servicing for back-focus issues, I find that unless I pixel peep, and is it really necessary to do so?, its image is very close to the 70-200 f/2.8 IQ without the weight. Clearly the subject isolation qualities of the f/2.8 aren't there but I guess that's the compromise part of the equation.
I keep saying to my wife, gee Tamron 20-70 f/2.8 would be a nice addition to my bag, but then I ask myself, why do I want to carry 2-3 lenses on a hike etc. when one does the job very nicely. Again like oher comments indicate, the 18-200mm is the goto lens.