Funny story. I've never had ANYTHING to complain about the Mark II. In fact it's the best camera I own.
Great, I MEAN GREAT IMAGE QUALITY;
never had much problem with AF, you just have to learn how to use it;
battery life is great;
LCD is great;
body is built like a rock;
video is GREAT for what it is... (and I run two webshows based on it)
So I don't see much of a point upgrading to the Mark III.
Most stablished 35mm photographers that I know and own a half-life Mark II agrees with me.
Can't see this being a big hit.
The reason some people are dissatisfied with the 5D is because they shoot wildlife, weddings, sports, photojournalism. All of these demand many AF points, and at times fast frame rate. Not all types of photography require these two things. But if you make a living shooting these subjects, then you need these features.
Pair this with the fact that Nikon's competitor to the 5D has a faster frame rate (with grip) and many more AF points. Also Canon's next cheapest camera the 7D is packed with features, but is only a crop sensor. It's tough knowing that you can pay a similar price or less to have these features.
Also there is the issue that the 5D has arguably the best image quality from Canon's line. On the other hand, the 1D and 1Ds have a top level features, where the 5D lacks severely. Now you end up having to choose high quality image vs. high level features.
That's my $1 (my opinion is worth more than two cents)