Upload & Sell: Off
That's the one thing that Zeiss couldn't exorcise from their 35mm line, Otus included- though one could accept the extra vignetting as part of their signature 'look', and it can usually be corrected easy enough.
Still, definitely glad Sigma saw fit to try and tackle it, though it is a little worse in the Art than it was in the EX.
Zeiss could have exorcised it, at the expense of either i) a higher price tag for the same resolution and contrast across the field; or ii) a drop in resolution and contrast at the same (or lower) price tag.
Hence the Sigma.