This might be of interest:
http://www.photozone.de/8Reviews/len...0_28/index.htm
Here is what Klaus has to say:
Quote: It took me 4 (f-o-u-r) samples of the lens to get a good one - please note: "good", not a "great" sample. The first three variants showed rather hefty centering defects which spoiled the results quite a bit.
As I understand it L means pro-build, but not necessarily premium optics. Nikon also have issues with quality control.