I tried 18-200 Sigma lens before; the one without the OS.
Yes, it did crank up at some of the shots, but I had printed out A4 size and I would say the results is acceptable.
I had sold it off last year, as I was planning to switch to the OS version but it was a long wait and I bought the 17-70mm f2.8-4.5 then.
Frankly, I do miss the 18-200 when I go travelling, it's great to have one which helps to capture many moments.
If you have you own sweet time to stake out at a spot to wait for the perfect moment, yes, go get a better lens and take the whole day to change the lens.
But unfortunately, I don't have. Hence I still prefer to get another SuperZoom - btw, Sigma had announced one with HSM version. 18-200 DC HSM OS. Check it up.