I have *terrible* luck with Canon L's....
Some examples with brand new lenses (some issues over multiple copies)...
70-200 II - decentering, broken IS, build quality issues, scratched front element, excessive CA.
35L - USM squealing.
24-70 II - decentered, scratched front element.
16-35 II - USM high pitch squealing.
17-40 - decentering.
I am sure there are more I am forgetting... I almost expect to go through a few to get good a good copy. The 16-35 issue is from yesterday! Waiting for my replacement copy now.