A few more comments on my 5d2 focusing issue situation. All based on using the 24-105L.
I've noticed that with the FF sensor and the focusing mode set to single, if you move the slightest amount, your pics come up soft. What's really happening is that the DOF is SOOO shallow that they're either back or front focused. This is even at f8 and higher. The DOF never seems to get any deeper.
Servo mode seems to have solved the soft focus problem. New images are tack sharp, but the DOF is soooo shallow even at F8 on the kit lens that it's hard to get a totally focused portrait type shot. It's frustrating that the one shot focus mode pretty much has to be on a tripod to stay sharp. If you have any tips, I'd appreciate it.
I don't know if this is normal and part of the learning curve of going from a 40d to the 5D2, but I highly doubt it. I'm not a total photography noob.