Here's another extreme example of lens damage and dust inside the lens, and how it affects image quality
http://www.lensrentals.com/blog/2008/10/front-element-scratchesGood of lensrentals to answer. I guess they didn't point you to Roger's blog?
Thanks. I read those before but it's been a while and for some reason I thought those were focused on a different aspect of things. The lens is sharp (tested against the 70-200 f/2.8 IS II and while a little bit behind held up well at f/4. The lens I'm returning is actually a TINY bit sharper than the other but I bought that one with the 15% off coupon so the $30 difference isn't worth it. Plus the lens I'm keeping is from this year so it also has the new Canon lens cap with the pinch in the center which I've to say I'm really liking much better. Thanks for everyone's help.