Bougth one recently. after test, found very soft at wide open. exchange one, better, still un acceptable. go to local Tamron service center , the guy told me this lens is very senstive for any knock. He recaliberated it. Now it is very sharp , comparble with my friend's Canon 24-70mm. Very happy with it.
Suggest everyone send the lens to Tamron for recaliberation if you found it is not sharp as most of review. And protect the lens carefully, any shock may make lens lost sharpness.