Canon EF-S 17-55mm f/2.8 IS USM

I have read several reviews of this lens. One of the few complaints I have read about is the build quality of this lens. How dust resistant is this lens? I am not a professional photographer but some of the places I will be useing this lens are in dusty conditions. This seems to be the perfect lens for me but I'm a little worried adout spending $1100 for a lens that may not resist dust very well. This will be my first major lens purchase. I'm not sure if I should buy this lens or look at an L lens. This lens seems to be a good focal legnth for my 1.6 crop factor camera,and I can really use the f/2.8.