as of right now, I only have 1 lens - Sigma 18-200mm and I am looking to add a second lens in the near future. I am looking at this one http://www.bhphotovideo.com/bnh/con...&sku=425812&is=USA&si=rev#anchorToReadReviews Canon 17-55mm f2.8 IS USM Anyoen have any experience with this lens? good? bad? I already know it is expensive and so far that would be the only bad I can think of.