I just received my tamron 17-50mm and its perfectly sharp in the centre but the edges are very soft. I know wide open is never great on any camera but should i expect from the tamron is the shot below at f2.8 50mm about right i is this not a great copy. There only other lens i have to compare with it is my nikon 50mm f1.4 which is better at the edges but thats to be expected with a prime surely.
http://imageshack.us/photo/my-images/337/dsc2162t.jpg/