For those of you who are satisfied with your 18-200 VR. You don't need this lens. I stuck with my f3.5-5.6 zoom for a long time because, heh, I took "good pictures". I adapted to low light, didn't miss f2.8. I was not convinced that a "pro" lens could make any difference visually...only if examining test shots of test patterns with a microscope.
I've been wrong before but this was a doozy. There is SUCH a HUGE visually noticable difference between shots made with this lens (and the 70-200 f2.8 VR) and my old stanby lenses that I about fell out of my office chair. My "good pictures" have become "great photographs". I now own both this and the 70-200. I sold my favorite lens of all time, a 24 mm prime, on a website. I'll never go back. You will get these two lenses from me when you pry them out of my cold dead fingers.
One more note. If you are like me and constantly read pro blogs and photo how-to books you will see most of the pros say something along the lines of "I don't use mid range zooms, I use wide angle for landscaps and long telephoto for close ups". I bought that for a while until I started looking closely at the metadata for photos they exhibit on their websites and books. Check it out, 6 times of 10, the lens is shown to be a 24-70 zoom. I use this lens almost exclusively for landscapes and lifestyle photos. I rarely go to a wider angle unless trying to make a visual "statement". So, here's one pro who says "I USE MID RANGE ZOOMS", and the Nikon 24-70 f/2.8 is usually the one on my D3 when I pick it up.