Mine did indeed arrive today
It comes in a little draw-string faux leather pouch like the DA limiteds, and the front cap is a nice tactile bayonet affair, rather than the rubbish push-on cap which comes with Pentax bodies. Overall it looks very high quality.
Autofocus with the DA*300 seems unaltered; it remains nicely decisive but not super-quick.
Image quality wide open appears to be good, but at the moment I have only done a few hand-held shots of wall charts. I will try to upload something when I get home from work.
Sadly, it does not work well at all with my Sigma 70-200/2.8 HSM. The AF functions, but just hunts back and forth aimlessly. I hope (and expect) it will do better with the DA*50-135....