First of all, the following survey results once again verified that SDM is indeed rather unreliable and vulnerable to break, although some fanboys would still argue that the sample size returned in that survey is yet "not enough to prove anything"!
http://www.pentaxforums.com/news/pentax-sdm-failure-survey-results.html
Quoted:-
"What is a little bit more alarming is the fact that three of Pentax's most popular lenses seem to have problems with SDM reliability."
Well, how dare PF is to make a statement like this?!
"If you're frightened by the AF issue, then Sigma has readily-available alternatives to all three lenses: a 17-50mm, 50-150mm, and 17-70mm."
My pardon? Are that Pentax glass so easily replaceable? And what's the point of using Pentax bodies but Sigma glass?!! >:-(
Btw, if there are still not enough of the reported cases, just view this online Pentax SDM Petition, then you should be convinced, if not yet!
Next, there is a new comparison review of the Pentax DA14/2.8 Vs the cheapo Samyang 14/2.8 lens. It is tested that there should be a design deficiency of the Pentax lens that the field curvature for far objects is always greater than DoF(!?) so that the whole frame of the image is always not sharp at somewhere in the frame, no matter how and where the user focused! :-o I now know why Jun was forced to retire after creating this lens! ;->