<p>Thank you for responses. I am surprised that many of you don't have dust issue as much. My 5D II came with oil stains to start with... and cleaning made it worth. It was a nightmare until I purchased oil stain cleaning fluid. After that a small dusts issue is only serious for wide angle (17-40mm, the wide end), which I use often for landscape. As some of you wrote, I am being careful when I change the lens. When I have to change the lenses outdoor, I'm always turned camera off, pointing down, protect from wind, and do it as quick as possible.<br /> Puppy Face, I live in dry static climate (Anchorage, Alaska), which explain a lot! Additionally, during the long cold winter, my windows are shut most of months, I'm sure it's dusty too. I would appreciate if you update me with climate info in your location.</p>