Hi,
I published some initial samples from my Sigma 12-24 EX on Pbase:
http://www.pbase.com/ekr/sigma_12_24These pictures are processed to a certain degree. Lateral chromatic aberration may have been reduced and sharpening may have been done.
In my impression the lens is quite OK. It does lack corner sharpness at least at 12 mm, but that is pretty extreme on full frame and the Alpha 900 used is quite demanding. For full resolution klick on "original" size.
Best regards
Erik