I have to say, I've not had anything to fault as far as Canon service is concerned, and to add, I'm not a CPS member here... requirements are simply too high for me, even though technically I meet all of them bar one.
Even under normal service conditions, they've been open and quick with turnaround. Usually within a week, for a simple lens calibration, though I did have a 16-35mm that took 3 1/2 weeks due to a major issue with one of the compound lenses assemblies splitting inside. Even then the lens was still in warrenty, but they made sure I knew what was going on at every stage.
I suppose here in Australia we're used to being given the ring around, but I've been satisfied with their service. Over all I've not been unhappy with their optics. I really enjoy my 50 f/1.2, and my 70-200L 2.8 IS is still my favourite lens, and most used.
My 16-35 however, has gone (I had the first version)... Corner performance was simply too low, and always had been on my 5D, and was simply exagerated too much on the 1Ds III. Even a problem on a full frame print. I don't need perfect (I actually have a 24-70 which is brillaint wide open, with a little red fringing on the outer edges), sharp with minimal distortion. I'm very happy with that performance.
I have however, been underwhelmed with a lot of their cheaper lenses. For me, I just want a lens that performs... If it doesn't, it goes.