Don't get me wrong, I LOVE my 5D. It's just that I didn't figure the 1.5 thing into my shutter speed, and it was low light ( i was shooting in a mode). So, when i went and did things properly, razor sharp, just like my film body. The filter I was using was a cheap UV filter. It may need cleaning, I haven't looked at it since removal. Just throwing some ideas out there for the original poster.
Glad to see some more KM owners on here.
edit: Have you tried it with the "beercan" yet? WOAH!!