Many people have put me questions about the 5D

It's another planet.
Starting with the bright and large viewer
and ending with the absence of the crop factor on our lenses (designed for 35mm, in fact)
I'd say in a word that APS sensor cameras (I have owned D60, Rebel, 20D)
appear as "choked" to me now.

The large pixel size seems useful.
It allows lower software in-camera artifacts in toning and colouring
and images look more natural and transparent.

Noise at 3200 Iso resembles Tri-X, that means it's fine, and also beautiful to look at.

Canon RAW processing software is quick and friendly, finally.

(my first subjective impressions, of course)