A few weeks ago I traded in my Canon EF-S 17-85mm f/4.5-5.6 lens for a 1969 Nikkor-N 35mm f/1.4. Why? Because I was unhappy with the quality of the Canon product, and because I knew an older lens with good glass is just as good, if not better, than a new lens with decent glass. Who cares if it's Nikon or Canon. I love my 20D and I knew it could really shine with a good piece of glass. Plus, this thing opens up to f/1.4.
So I purchased the lens for a fair price, and got a Nikon F mount to Canon EF mount adapter with AF confirm chip from Hong Kong and mounted that hunk of glass on my Canon 20D. Great for portraits, low light, walkabout, and gotta love that shallow DOF.