In some ways, this is a surprising thread for reasonably intelligent people to be engaged in. We all know, for example, that there is no such thing as absolute perfection. Yet we look for it and expect it. Moreover, we tend to measure how close we come to it in our "stuff" by the amount of money we pay for the stuff. We do this with cars, houses, gadgets and . . . cameras and their accessories. We pay $65-75K for a BMW or Merc and expect that it will never break down, get 60 MPG while carrying all sorts of loads at all sorts of speeds. Nevermind that the $800,000 someone might pay for a Rolls or Bentley or Ferrari also gets the buyer an occasional breakdown. So it is, I think, with our photo gear. When we put down $2500 for a new lens or $3500 for a new body, we expect them to be perfect. After all, we argue, we paid 'top dollar'! Nevermind that there are lenses out there that cost 4-5 times what ours did, and even they are not perfect, have an occasional flaw, etc. They are no more than a collection of hundreds of mechanical parts that are supposed to work together, but sometimes do not. No matter what some of us might like to believe, there is no such thing as absolute perfection.
To put it another way, we want, and expect, far more than we are willing to pay for. If we are willing to pay $7500 or $10K or more for a completely hand built lens, in which all the components are hand made, individually tested prior to assembly then hand assembled and tested, adjusted and retested, we might come closer to perfection. But, alas, we're not willing to pay for all that.
I agree with pdirestajr in reply#27 and victorwol in #31 above. Our expectations, for the price we are willing to pay, are flatly unreal. Seems to me that we get a pretty good product from Canon for the prices we pay. Let's stop carping and get on with the business and enjoyment of taking pictures.
As for me, I now own 6 L lenses, have bought and sold 1/2 dozen more as my needs have changed, mounted at times on a 50D, then a 5D2 and now a 5D3, and have never had a problem with any of them.
Best wishes to all.