I heard of Canon reps suggesting against filter use for the general loss of IQ... then again, there are lenses that aren't fully weather sealed without a filter, and of course Canon doesn't make screw on filters anymore (or do they? They certainly aren't in the stores).
Also thing with filters, you might lose more light, and increase the chance of internal reflections with putting so many over each other. My Canon 50mm 1.4 had a Tiffen filter on it at first but that caused bright lights to reflect back from the sensor onto the filter and back in again.