Yes, 18-200mm is a really good "shoot everything" lens. But do u mind the weight factor? How about taking pictures in low light environment, is ur lens fast enough?
I really recommend u to use ur kit lens as an estimation of what kind of lens and approxmiately how much of a focal length do u need, go thru ur old photos.
Do u find that u are having a hard time in low light situations? At what focal length do you usually shoot and do you find that it limits ur creativity or urge to take nicer pictures? so do you really need the extra focal length then?
I have a fren who bght the 18-200mm lens as his starter kit, ended up selling it off after 2-3mths. Its a good lens, like 3 in 1 kopi. But he prefer having a faster lens with shorter focal length as he shoots @ 70mm and below normally for street shots.
In the end he bght the 55-200mm kit lens and bght a Tamron 17-50, with the cheapo godlike prime AF 50mm F1.8D, he had no trouble shooting in low light situations and ocasionally covering the object thats in the 150mm focal length range with his 55-200mm.
Some budget calculation of my fren's lens - 18-200 @ $ 1100 after selling he got back $900, Bought the 50mm prime@ $175(1st hand), the tamron 17-50@ $630(1st hand), 55-200mm VR@ $250(2nd hand) which adds up to $1055.
So ask yourself what do u really need?