<Albert, why aren't you enjoying you CZ on canon experience? seems contrary to 'popular' opinion..?>
1. I don't have a full frame body
2. I don't have any existing collection of C/Y lens, the price for any of those exotic C/Y lens, like 21mm, are so expensive and hard to find. So so C/Y lenses are not that much better than Canon primes (like 35 f/1.4, 85 f/1.2 or 135 f/2) with all things considered (AF, Metering).
3. I use Canon gear mainly for wedding. So I need something fast. Anything else I tend to use my ND nowadays. When I first got my 20D with the 17-85IS, I really love it. I could never put it down since the image of 20D is so clean especially in hi ISO, AF was so fast and accurate comparing to Contax, the E-TTL II just blow my mind, and the 17-85IS lens is really nice walk-around/travel lens.
4. Popular opinion has two sides, you hear many said how great the C/Y + Canon combo is, and it is all true. But a lot of time I see the same group of people sold their C/Y lens eventually and buy back Canon glasses, or move into Leica. Yes, the popular trend is onto Leica now.
5. I spent a lot of time considering and researching the C/Y Canon opinion. I know how great the CZ lenses are, and very unhappy the color & bokeh of Canon lenses. In the end, I decided to keep my funds for a future digital back for my C645. Then I can use the AF CZ lenses I already own.
6. It is all personal. But I do envy the people that uses C/Y lenses on their Canon body and produce great images.