Earlier in this thread BigMackCam noted that Steve Cicala of Lensrentals had some worthile things to say about lens quality.
Here's a link to one of his better blog entries on the subject, which I feel is well worth reading:
Lens Rentals | Blog
Back in the film days, I became concerned that I was becoming *too* obsessed with lens quality and started to experiment with cameras and lenses that were - to put it mildly - less than perfect. I shot with Holgas, Argus C3 and C4, Agfa folding cameras, CZJ Tessars and others and found that they could *all* produce beautiful images, limited only by my artistic abilities. Ok, so shooting with the Holga was a bit more of a challenge, but it could still produce arresting images when shooting the right subject in the right conditions.
I decided to not worry about whether a lens is *the best* or not, and instead concentrated on capturing beauty in my photos.