The 5D Mark II is a god of a camera. Really. It is magnificent. People do complain about the focusing, but I find it good enough most of the time - also, I shoot fast paced weddings and low light receptions, events, children and live gigs (in terrible lighting). It’s really all about knowing how to focus. A lot of people expect the camera to just focus on anything you point it at.

The camera is able to focus on things through latching onto contrasting/rigid lines. If you know that, focusing becomes a lot easier. For instance, if you’re shooting a live gig and the musician in front of you is a black blob silhouetted by magnificently powerful lighting, you can’t expect the camera to try and focus on “nothing” by focusing on the center of that blob. You need to actually find the contrast line of their face to focus on.

I really think that around 70% of people who complain about the 5D Mark II’s focusing problems are people who have bad technique when using spot-focusing.

That being said, the 5D Mark II is certainly a tad bit worse at focusing in low light than the D700 is, as well as the 50D or 7D (from my experience). The 5D Mark III is quite incredible at low light focusing, apparently, but I can’t be sure until I’ve had one in my hands.

I still believe that you can mitigate most focusing “issues” with the 5D Mark II by having better technique, and becoming very good at anticipating events.