Hi Glassman,
I'm glad you're asking about this, because I JUST went through this exact same question. I was upgrading from a D60 to a D90, and since I sold the D60 as a kit, the 18-55 VR went with it. I already had the 55-200 VR but though that maybe now would be a good time to sell the 55-200 and just go the 18-200 route.
Long story short, after playing with both lenses, this is what it comes down to: photo quality vs. convenience.
As it was said to me, the 18-200 is a "Jack of all trades, and a master of none". To be able to give you the full range from 18-200, Nikon had to sacrifice some image quality in the process. The 18-200, while a decent lens, has major corner sharpness fall-off; which was just too much for me, and I'm not even that serious of a hobbiest. In my opinion, for the money I would have dumped into the 18-200, I wouldn't be getting images I'd be satisfied with.
You'd be much better off going with the 18-105 VR; which is what I went with. Comparatively, the images are much better, and the fall-off is much less. You could go with a 18-55 and a 55-200, which would be the most cost effective and best image wise, but I love the 18-105 and 55-200 combo. The 55-105 overlap is nice, and you really won't be changing your lenses as much as you might think.
The new 55-300 or 70-300 is also an option outside of the 55-200, but I haven't used either.
However, none of these lenses are 2.8 lenses, which is my next direction. I would rather have saved a little more and gotten some good 2.8 glass, but I had nothing below 55 except for the Nikon 35 1.8. I'm eyeing the Sigma 70-200 2.8 II. Just waiting for a good sale, lol.
Lemme know if you have any other questions! Good luck! Let us know what you decide!
Kevin