Nothing about the 17-85 IS is actually good. Colour and contrast are disappointing, the chromatic aberations don't help there either. A lot of barrel distortion. It is one of Canon's weakest lenses, which is a shame.
If you NEED IS, then consider the expensive but very good 17-55 f2.8 IS, or the 28-135 IS (and get a wide angle lens to complement it, like a Tokina 12-24 f4).
Else, consider the new Sigma 18-50 f2.8 macro, the Tokina 16-50 f2.8, or even the Tamron 17-50 f2.8.
If you want the silent and fast USM, the 17-40 f4 L is an option. On a 350D/XT it will focus more accurately than the above trio.
Weather sealing is not a pro, only if you have a weather sealed 1D DSLR (and you are yourself ok making photos in streaming rain).
My advice: avoid the 17-85 IS. It gives lacklustre results. Even the cheap 28-105 f3.5-4.5 USM II is a much better choice, again pair it with a wideangle zoom like Sigma 10-20 f4-5.6, Tokina 12-24 f4, Canon 10-22 f3.5-4.5 USM).