Wanting to have a light kit for four months on the (rail)roads in Europe, I acquired a Canon XTi, 10-22mm zoom, the 17-85 IS zoom and 70-300 USM III IS zoom. I got them all in the six months before going and tested them thoroughly in my typical shooting of flowers, scenery, animals and grandkids.
On the trip I was surprised at how tough the little XTi was--and how good the sensor. Another surprise was the fact that the 17-85mm was used virtually all the time. The wide zoom was used for about ten percent of the 8600 images I shot and the 70-300 very rarely. If I were to go on another such journey, I would not hesitate to use the 17-85mm IS lens on an APS-sensor Canon as my only lens--it proved to be that good. I might add a polarising filter for reducing reflections and a walking stick and small beanbag for those places where monopods are not welcomed.
The photos have proved stunning, whether macro, panoramic scenes or street scenes. The European Union has passed some rather stringent rules protecting a person's rights to their own image, so you have to be careful not to do closeups of individuals without permission or you will be explaining very quickly that you are not shooting for commercial purposes.
I've seen many comparisons where this lens is not rated as highly as the L glass, but even in this computer-crafted technology, there are individual lenses that rise above the standard or sink below it. Perhaps I've always been lucky, because I've never been disappointed by Canon.