It's the kind of surprise a person has when someone says they're going to hit you if you poke them one more time and then you poke them.
I've heard Google is working on something similar for Android and I really hope it happens sooner rather than later.
The CM installation process has gotten way easier (you now don't even need to wipe your phone or lose any data - it installs right on top of the stock ROM), so there's really very little reason not to use it over stock if your device is supported, IMHO.