I bought my girlfriend a Sigma 70-300 DG Macro today for her Nikon D40 (I know...I tried to convince her into an XTI, but she really likes the smaller size). Anyway, we went to the zoo to test it out, and I was honestly kinda shocked. The sharpness, contrast, and just about anything that a non-pixel-peeper would ever notice was right on par with my Canon 70-200 f/4L. I know there are definitely things that the Canon has going for it (build quality, smoother rings, amazing auto-focus, and quality-control for individual copies), but I'm seeing some really compelling reasons to pick up the Sigma (the extra 100mm at the end, macro, light weight, and the price tag). The lens is only $150 including tax, and I'd dare say there aren't many more versatile lenses at that price point. I'm considering selling my Canon for this lens and putting the difference into an 85mm f/1.8. I'm not meaning to bash the Canon lens or even put the Sigma on it's same level, but I'm just offering out the suggestion for the Sigma being an excellent alternative for those who aren't sure if they can justify the price of the Canon.