After coming from a 1D to the 5D2 i was massively dissapointed with the AF on the 5D2
especially the AI servo and outer point ability to even get a lock in low light let alone track anything
Neuro suggested turning on the 6 assist points (I have no idea why these are off by default)
I found this helps AI servo alot in good light
in low light I dont even atempt to use AI servo and I dont bother with the out points just use the center point and recompose. With f2.8 lenses the center point is pretty good.
But even in good light i have just stopped using the outer points just because I have gotten used to using the center point only even if i dont have time to recompose the 21MP gives enough resolution to crop for a better composition. I've even stopped using the outer points on the 1D just because I have modified my shooting style to centerpoint and recompose.
Adding a manual focus screen and using manual focus also fixes many AF issues
I am really looking forward to these next gen 5D cameras with Pro AF then I change my shooting style back
I would rather not have to concentrate on workarounds for the limitations of the AF system