I wholeheartedly agree with this thread.
I only buy new gear. These lenses/bodies have been defective:
300 F4 L IS (severe front focus that took three trips to fix)
17-40L (would not focus past 30mm. Took two trips to resolve)
70-300 IS (portrait orientation issue, recalled by Canon)
7D (severe focus issues, took two trips to repair. Right LCD zoom button stuck after two days also)
70-200 F4 L (front focus issues, one trip to repair)
17-55 IS (IS died within one year)
50 1.4 (AF died within one year, and died again within one year)
Almost every Canon lens I buy requires micro focus adjust. I just don't trust them. I have so much invested in their gear, that I don't want to leave. But I really wish they'd join the rest of the industry and offer four year warranties if they're not going to perform quality control tests before shipping units.
I still can't believe they're selling $10,000 lenses with a one year warranty. That's inexcusable.
I own or have owned 4 of the listed items and never had an issue (maybe it's hit or miss quality control) and don't need MA for any of the lenses 50 1.4, 70-200f4 or 17-40. But I can say that i've had problems with a Nikon d7000, 35mm 1.8... Both several trips to a very UNHELPFUL Nikon before supposedly fixing them... Yes I sold my Nikon stuff and came to Canon. Canon is NOT the only company who releases "problematic" cameras and lenses (if you want to call them that). If you believe a longer warranty is in need for a 10,000 lens, I cannot argue with that! But my point is just that Canon is one of 1000s of companies that do have little issues. Canon is ranked much higher than Nikon in customer service satisfaction and I understand why... Dealing with Nikon was worse than pulling teeth.
That said, I'm sorry about your issues with those lenses and 7d... I'd be pissed too.
of course these types of scores could be biased... but I have found it to be accurate IN MY EXPERIENCE