Elliot Bernstein , May 29, 2007; 01:47 p.m.
The only reason to switch would be if you don't like changing lenses.
If you hate changing lenses, you will love the 18-200. If money is not an issue, you will love the 18-200.
Your best bet would be to try the 18-200 lens out for yourself and compare picture quality with what you now have. You likely won't see a difference unless you take out a magnifying glass, and even then, the diffences if any will be very, very small.