Since Pentax made the SDM AF motor, the SDMs in various DA* lenses have been reported death by different users from time to time. In fact, such reports have never stopped. Recently, the death reports of SDMs have been about the DA 17-70. Examples:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=33624008
http://www.dchome.net/viewthread.php?tid=778328
(Post in Traditional Chinese, or read the Google Translation Here)
So, the poor reliability of the SDMs really upset so many users and also put off quite some potential buyers as well, like what this guy tells. I think unless Pentax "improve" (actually debug) their SDM design to make it works more reliably (not even to mention to make it run faster), nobody would trust the SDM! (yet an example)