Hi there!
I am quite suprised to read that the 2,0/28 is not sharp at infinity. I can only say that since I have this exciting lens I do most pics at full aperture - and no sign that there is something not really sharp. When taking available light pics this lens is a must. I cannot agree to Michael on another point: before the 2,0 I had the 2,8. When using the 2,0 at 2,8 it is better, no light fall off, and a better sharpness. So I sold the 2,8 and waited to get a 2,0.
Best regards
Wolfgang