I've the 17-85IS and I find it a great go-anywhere lens. It is a jack of all trades therefore do expect some limitations in the form of distortion at the wide end. But I don't find it too offensive. This is my first 'standard' dSLR zoom, so I have nothing to compare it to only my Sigma 24-70 f/2.8 which again shows some distortion at the wide end and it's much heftier than the 17-85IS. That's not to say the 17-85IS isn't well put together as it is and it will do me for a good few years.
-------------------- Master of the Bench and Global Ambassador of the Brotherhood of the Bench Bench or No Bench