I just received the Sigma 17-50mm and so far ...I am lovin' it!!!!!!!! I know it's super early to be REAL sure but so far, taken random shots around the house and on a micro-adjustment sheet I have that I printed from online, everything is looking really, really sharp (even at 2.8) with no focusing issues showing up so far! I may be on the road to loving it just as much as my Sigma 85mm. Definitely more than the tammy and it's running a tight race with the Canon 17-55mm (I know hard to believe)! Corner softness seems to be the issue with this lens from all I have read so I will have to check that out more closely but I don't think that will bother me too much anyway unless it is really bad!