From what I have read in other forums, the 18-200 is a dandy lens, but as it's price point suggests, it may not be sturdy enough for pro use. Now I personally have never understood that term, as I'm a pro and have never broken a camera, and I've used FMs and 8008s and N90s and D70s for paying jobs.

I imagine if you are hard on gear, take it into difficult places, it might be a bit delicate for that, but if you're shooting weddings or semi-controlled situations, it should be fine.