Sounds like people are pointing towards the wide end--if the Tamron 17-50 has output as nice as the 28-75, you could save a ton vs. the DA* 16-50.
The famous Prodigital2000 has 3 of them for $299US (each
) obo right now:
NEW TAMRON AF 17-50mm XR F/2.8 Di II LENS PENTAX K20D - (eBay.ca item 310105699056 end time 01-Jan-09 14:06:07 EST)
They'll probably take $270, so I'd start with an offer. Less than half of the DA*16-50.
I was thinking the 28-75 because I like the long end not so much for the reach, but for the foreshortening for portraits.