Autofocus:
As I have mentioned before, there are 62 custom functions meant for various situations. Canon has made a Canon has said that they have comprehensively redesigned the AF system of the 1D Mark IV. “The EOS-1D Mark IV's AF system has been comprehensively reconsidered from its design components (sensor, firmware and mechanism) to its manufacturing execution. The design objectives were improved stability, reliability, precision and function. These objectives have been achieved with a totally new AF system, featuring totally new AF hardware and incamera software. The result is a highly intelligent, fast, customizable and solid professional
autofocus system that is both stable and responsive”.
The Mark IV has the 45 AF points as the 1D Mark III and the 1D Mark II. However, the Mark IV has 39 cross type autofocus points that are sensitive to f2.8 and faster EF lenses. In comparision, the 1D Mark III had 19 cross type sensors and my beloved 1D Mark II had 7. If you want details about it, then you may please download the canon discussion paper. You can find it here:
I had the camera in my hand but could not immediately rush to a forest due to my office schedule. I rushed to a bird sanctuary 100 kms away from my home to test whatever I could find.
The Mark IV has various options to customize. Till date, I have been happy with the autofocus. Initially, I was a bit worried when the camera picked up the water instead of the bird. However, after reducing the sensitivity settings from default to slow, the issue got sorted out.

What is not so good:
There are enough people out there to prove that Canon has got it wrong. A David vs Goliath is always a good news story. Frankly speaking till date, there is nothing which can be mentioned as bad. So mentioning a few challengest that needs to be overcome.
Ergonomics for Video:
The Digital SLRs were not designed for movies. So adapting the movie mode ensures that there are some compromises to be done. The chief among those is in ergonomics.
When you use the movie mode, the viewfinder is off and all the viewing has to be done through the lcd at the back. Imagine yourself to be handholding an intermediate lens or a medium telephoto lens like a 70-200 and trying to shoot a movie clip of an elephant herd. You have to now hold the camera and lens combo at arms length so that you can look at the lcd and do the focussing. The autofocus during movie shooting is too slow and bad. You have to use manual focusing and it is not easy to look at the lcd and focus. Well, which professional movie maker users auto focusing while movie making? However, the ergonomics of movie cameras/ camcorders is different. So it is better to use on a tripod or a lcd viewfinder or both. This is not an issue specific to canon. It is a legacy of our Digital SLRs. More about this later.
Auto Gain Control in Video: I checked the movie mode by shooting a few clips. The internal microphone picks up lot of Image stabilization noise. Of course, Canon has mentioned that the internal microphone would pick up these sounds. Canon has provided a port for external microphone. Unfortunately, there is no option to control auto gain control ie. the camera will automatically amplify the sounds. For advanced film making, this is an issue. Remember, that this camera is going to be used not only for wildlife photography, but also for making corporate films, music videos, wildlife film making etc. More about videos later.
AF-on button in vertical: If you use the AF-on button at the back to do the autofocussing instead of pressing the shutter speed, then there is a surprise for you. I realized that couple of times I accidentally pressed the AF-on button on the vertical grip. Frankly speaking, this is by no means a major issue. I just shut off the vertical grip and for scenes where I need to quickly change to vertical orientation, I moved the camera clockwise and clicked with the horizontal shutter button. After reading this you can realise how hard I am trying to find a "problem".
Shifting from still shooting to movie clips is easier. I have customized the FEL lock for videos. Press it and it immediately starts recording. However, the problem is videos require much slower shutter speeds. You can pause the movie shooting to take stills by completely depressing the shutter button. Or you can stop the movie shooting and shift to stills. However, you have to immediately change the shutter speed. That is an immediate challenge that needs to overcome.

This camera is the best in Canon's line up till now. If you can't get your shots with this camera, then you are not likely to get it with any other camera. Highly Recommended for anyone who takes their photography seriously, for professionals and for people who want to make video clips as well.