I own the original version of this lens and used it on 3 different bodies for the last 3 years: D5000, D300 and now D7000.
I have no idea what some of the above users are talking about saying it is Nikon's worst lens in any way.
It is convenient and it does have distortions at 18mm and it is a little soft at 200mm.
It is a GREAT travel lens and, even for a professional (in the sens of very demanding in quality) travel photographer, this can be a very good lens if used correctly.
I use it between 35mm and 180mm, usually at F8 as it give very good contrast and sharpness. Of course, I also apply lens correction in Lightroom (something that I do not have to do for my 105 mm f/2.8 for example, but that's a prime, full frame lens which is a total different story).
I bought the 18-200 as a replacement for the set 18-55 + 55 -200mm and I never regret it.
Who compares this lens with any f/2.8 models or with a lens designed for full frame is just wrong!
Oh, and of course it's almost useless in low-light! It IS a 3.5-5.6 lens! Why would you expect something else?
There 2 things that I don't like too much: "zoom creep" which can be solved easily and the relative cheap construction (the rubber band used for zoom came loose after 3 years while using the lens in Mexico in extreme heat for 6 days in a row!) - none of these has impact on image quality anyway.
These are some of the photographs I like best, taken by me with my the 18-200mm:
Adi Chiru - Portfolio, Fine Art Photography, Nature and Wildlife Photography, Travel Photography, Family portraiture | Nature | Green (I think it's quite sharp here! the image was not cropped)
Adi Chiru - Portfolio, Fine Art Photography, Nature and Wildlife Photography, Travel Photography, Family portraiture | Nature | Green (what is so bad about this bokeh example?!)
Adi Chiru - Portfolio, Fine Art Photography, Nature and Wildlife Photography, Travel Photography, Family portraiture | People | Photo 1 (this was at 5.6 at 200mm - maybe I am biased but there is very good skin tone here, very good texture in the hair and it was shot hand-held while the subjects were in motion)
Adi Chiru - Portfolio, Fine Art Photography, Nature and Wildlife Photography, Travel Photography, Family portraiture | People | Photo 1 (again, good colors, very good detail, very nice DoF...)
As many reviewers already stated many times, it a the best lens in its category. The links posted above by Derrel will indeed help you figure this out. Of course, Ken Rockwell is who he is but in lenses, for me, he never went wrong yet...