[MaximusJ]

I'm not using a Canon and I dont own a pro-sumer body so I cant really talk about something I dont know.

On my D7000, even if you're in focus, the camera still check for focus when you press the shutter button completely (if the shutter is in AF Priority; thus the little delay. Maybe half a second was exaggerated, but you get the point). When using back focus with the shutter in shutter priority, the camera then snaps the shot, regardless of the focus. That means if you know you're in focus, you dont have to ask the camera to double check before proceeding with the shutter.

I'm comparing Shutter button focus w/ AF priority vs. Back focus w/ Shutter priority. One is faster then the other (On DX Nikons at least) unless I'm missing something?