Personally I think people have been so brainwashed about the 5DII AF system that even when presented withevidence to the contrary are in total denial. A can do frame of mind is needed to turn this into a will do reality - instead of a 'any other camera' is NEEDED to capture something moving.
I wonder how many people who quote the 'useless' AF system have had real hands on experience without the use of a 'pro' AF system ie a 7D and a 5DII?
I wonder how many people HAVE to have the latest and greatest before they believe that a halfway decent photo can be taken? Yet week in week out we see evidence of first class images produced on older technology - such as the 5D classic, 20D, 450D and the like
First off, shooting a photo of a sitting dog in low light is an entirely different story than shooting a fast moving bird that can and does change direction on a dime in low light just after sunset. For the record, I own both a 450D (which has an AF system about the same as the 5D II) and a 7D. I spent a LONG time trying to shoot birds with my 450D, most of the time right around sunset as my day job would never let me get out there sooner to shoot during broad daylight. I pushed that camera to the absolute limits, and it did ok, but I never once got a shot that I could call "professional". Within a week of owning and using the 7D, I was getting shots that I stopped dreaming were possible. Still nothing I would really call professional, not on the level of Art Morris and similar photographers, but good enough that I actually believe I can improve my skill and one day soon call some of my shots "professional".
There IS a difference with AF systems when it comes to AI Servo tracking performance, particularly when you have more higher-precision cross-type points. With the 450D, the camera would spend too much time trying to find that focus lock. I either missed focus completely because it would give up, or I wouldn't nail focus where I wanted it, and the key part of my subject would be just barely, but noticeably, out of focus. Since there was only one cross-type point in the center, it was difficult to track a moving bird across the sky where it may not always be dead on the center point. The advancements the 7D brought to the table were more than simply 19 cross-type points with broad frame spread, though. It brought some extremely useful dynamic point expansion features and configuration options that helped me tune the camera such that it could keep focus on my active subject, even if it moved away from the primary selected point. The 450D does not offer any of these options. Having experimented with the 5D II, it seems it has six AF assist points around only the center point that behave similarly to the 7D's point expansion mode, which is handy for center-point focus. The 7D brings that capability to any of its 19 AF points, along with a variety of other point selection modes that allow you to tune AF to different circumstances. I've used a friends 500D for AF tracking as well, and its about the same as the 450D, although it is certainly more usable in lower light with an extra stop of ISO.
So yes, I have used older Canon cameras that have far simpler AF systems. And I offer a resounding "Absolutely" to the fact that a more advanced AF system can offer a world of difference in whether you nail focus, or miss it by a mile, and how frequently you do so. The 450D could get it some of the time, the 7D gets it much more often than not. I would hope that a top-shelf PRO AF system would nail it 90% of the time or more for the money you spend on one.
No one has said the 5D II system is incapable of AF, but its a far cry from extremely capable
for high speed, mid to low light action (i.e. bird photography at sunset, sports action indoors, etc.) I figure there are two ways to improve that...either stuff in more single-line AF points so they act like a net, or improve the precision of fewer points. Nikon's taken the brute force approach of packing in as many AF points as possible. Canon has taken the selective approach by making all points cross-type (and with the 1D X, they've taken a blend of both approaches.) There is no way you can claim that the 5D Mark II 9-pt/6-pt hidden assist AF system is a "professional" grade AF system...not compared to the 7D (for a low-end pro-grade AF system), and certainly not to any of the 1D line AF systems from the past 4 years or so. I'd be willing to put money on just about any current Nikon AF system, on a professional body or not, outperforming the 5D II's in any strenuous exercise.
I don't think its unacceptable to ask Canon to put an AF system on the 5D that correlates with its position in the Canon DSLR lineup. Its long held status as the pro body with marginally better AF than Canon's entry-level DSLR's, not even ranking as good as an xxD with their 9 cross-type points, and was considerably lacking compared to the 7D. Its understandable that the 7D would surpass the 5D line for a while given that its a newer body, but I don't think thats an acceptable thing for the long haul....the 5D deserves better than a bare-bones 9pt AF system with a single cross-type center point...and so do those who intend to spend $3500 or very nearly so street on the 5D III when its released.
So I really hope that the 61pt AF is real, I sincerely hope it gets 21 center cross-type points, and I truly believe the 5D III deserves at least the 100k RGB metering sensor, even if the advanced AF hooks the 1D X has are absent. I'd feel good about spending $3500 at least if that was what I was getting...it would feel legit, and worth while. I had a very hard time justifying the 5D II, and in the end I never could...for two years I've been playing with it in stores, borrowing from friends or other photographers out in the field to give it a try, drooling over it online...but I couldn't pull the trigger. Between the rumors about terrible fixed-pattern read noise at low ISO, and the extremely lackluster AF system...it just wasn't worth it. Given how the 7D has made it possible for me to finally start exploring the bird photography I've been floundering with for the same amount of time, I feel good about buying it, feel it was well worth the price, and am a true believer that AF systems do matter.