Originally Posted by dugrant153 
hehe... would you describe the MF feel as "sandy" or difficult to move?
As for the corner sharpness lost, I think this may be exhibited on my Sigma 24 F2.8, which (even when stopped down to F4) is very soft on one area. It could be a lens element out of alignment also. hmm...
By poor edge quality... does this mean that if my subject is in the corner, he/she/it will be strangely soft?
MF is definitely "sandy."
By edge quality, I don't mean just a reduction in sharpness, but actual distortion. For an example, see the corners and edge of the shot below.
Check out the difference between the center and the edges (look for the triangular windows in the buildings caused by distortion: downtown is sharp, east and west midtown is not)