I use back-button AF. Great for birds (bump-focus), useful for focus recompose. Only downside is if you hand your camera to someone else, but green-square mode cancels back-button AF.
Ditto! And whenver I hand my camera to someone else, I always take the opportunity to teach them about rear-button AF so they can be cool to.
Personally, though, I remap AF-On and * functions. The * button is vastly more convenient for me as an AF on button. I don't use AE lock all that much, so I assign it to AF-On, which is kind of weird to reach given how it is depressed a little relative to the * button. (BTW, this is on a 7D right now.)
I honestly couldn't live without rear-button AF anymore. I live and die by AI Servo mode...the only times my camera comes out of AI Servo are when I'm doing astrophotography.