I really want to get the 24-70 f2.8L but there are numerous accounts of poor quality control. Is it really that common? Is it going to be a roll of the dice, even though it's a $1100 lens? The good copies are stellar, but I see a lot of threads on dpreview of people saying they got a bad copy, had to get it calibrated. Often times, they wouldn't get a working lens until it was replaced entirely. Should I just not even bother, and stick with other lenses? I was planning on using this for like 90% of my shots.