Photozone test:
http://www.photozone.de/nikon--nikk...m-f35-56-g-if-ed-vr-ii-dx-review--test-report
I bought a Tamron 18-200 (in Pentax mount) for a round the world trip. Unfortunately, that lens had some seriously soft corners at 18mm f3.5, which was where I took a goodly fraction of my pictures (I know more about photography now). This lens doesn't seem to have crazy soft corners, but the Nikon has 4.1% barrel distortion at 18mm, which is a lot. You can rectify that post-processing, but that will reduce your overall sharpness.
All in all, superzooms tend to require a lot of light for good image quality, as you'll probably want to stop them down to ~f8. And of course, they're generally best in the middle of their zoom range. And probably won't win any bokeh contest. But they're sure versatile when it comes to range. I was happy to have mine, though I don't use it a lot now.
Ken Rockwell sure likes his, though:
http://www.kenrockwell.com/nikon/18200.htm
http://www.kenrockwell.com/nikon/18-200mm-ii.htm