There are reports at Nikonians and DPReview forums that there may be more to the new Nikon D200 firmware upgrade than what Nikon has originally reported. Sigma lenses on Nikon D200 bodies could only be focused by half pressing the shutter button, the AF-ON button did not work. The only solution until now was to send the lens back to Sigma for them to correct the issue. Well the new firmware now seems to have corrected that issue. Other people have reported that AF speed has improved and get this VR (Vibration Reduction) lenses seem to be behaving better after the firmware upgrade as well.
I have not upgraded my D200 yet (being in the computer world I like to let others go for it before I take the plunge) so I will be going for it this weekend and report back my results here with the 70-200VR, stay tuned. =)