David, I don't know what your experience has been, but I have been using this lens extensively - took over 2000 shots with it in the past six weeks, and I think I have seen flare on about 4 photos, in situations where you would normally expect to get some flare no matter what the quality of the optics. So (1) I'm not sure what the fuss is about, and (2) Canon has said nothing about the cause of the so-called problem, correspondingly nothing about what kind of repair they will do, and nothing about what level of technician and quality control procedures will be adopted wherever it is being fixed. I think Canon should address these concerns, especially as they have been raised already.
Coming from the school of "if it ain't broke don't fix it", and I am so pleased with the resolution and contrast from this lens, I am loathe to have it tinkered with until I learn more about the above. All of this of course is "up-stream" of the issue about how long they will hold it once we send it there.