To be honest, I've never found the 5D's AF system to be *that* bad. In good light, the outer points are perfectly fine. In low light, you either use the centre point and focus/recompose, or use some kind of focus aid, like an ST-E2 or a Speedlite.
Like I said, it would have been nice for Canon to at least use the 40D/50D AF system in the 5DmkII, but the existing system isn't that bad (and the rest of the camera is terrific).
I'm sure it will work out just fine, but I am going to be using it primarily for weddings, so the light will more often than not be low. I will, however, be using fast glass though so that should help.
Does the ST-e2 shoot out a visible light to help with AF?