I'm so torn as to whether or not getting the Sigma 18-200 OS makes sense. Photozine.de reports it is soft at 35mm, but pretty good at 18, 50 and 200mm. The Pophoto.com review shows that it has better image quality at 200mm than the much acclaimed Nikon 18-200mm. Rick at "Fredmiranda.com":http://www.fredmiranda.com/forum/topic2/547490 reports the same thing, it is amazing at the ends of its range, but in the 35mm range, it is soft. This is apparently a design issue with the lense.
Still at $500 street it is pretty amazing.