i have vignetting on my 5dmk2 on my 60d zilch there will be vignetting on full frame i do use a filter in the rain or near salt water/sand but apart from that REMOVE THE FILTER DO NOT PUT CHEAP GLASS IN FRONT OF SUCH A BEAUTIFUL L LENS.
You must shoot a different kind of subject that I do. I don't have the luxury of shooting without filters while producing the images that I do. 75% of my photography involves filters of some kind, whether it's a UV/Clear when shooting out the window of an airplane, long exposures with ND to smooth water out, polarizer to add contrast to natural light. I shoot landscapes that get blown up big. The nature of my photography demands filtration. Do you know that not everyone shoots the same kind of subjects that you do, that for you it's easy to say "don't shoot with filters unless necessary". Then there are others like myself who find it necessary to use filters in most situations.
Do you also know that tiffen and schneider glass is of the same optical grade that your precious L lens is made out of? So it's not an issue of "cheap glass". Cheap glass also has nothing to do with this vignetting problem. It's the rim mount that is causing it. Clear glass doesn't make lenses vignette. Do you know why? It's clear!
And to head off those who want to scream "lee" or "cokin". I understand. I use a lee system whenever possible. But it's not always possible with what I shoot.
And the bottom line of this thread is that Canon should not be making $2400 long zoom lenses that accept threaded filters, but cause additional vignetting, especially since the old version of the lens didn't.