Here are the specs:

• 10 FPS
• 16.1 MP APS-H CMOS censor
• ISO Range Native: 100 up to 12,800 in 1/3 or 1/2 stop increments, with ISO Expansion: 50 and 25,600, 51,200, and 102,400. [Editor: Native is really the only one that should be looked at]
• Dual DIGIC 4 Processors [Editor: 16x more processing power than the DIGIC 3 system]
• M-RAW and S-RAW [Editer: Medium and small sized RAW files]
• Better Noise control
• Enhanced Custom Functions [Editor: Ok, now they're just reaching for more points, really? how enhanced are they? ]
• [Editor: Something about 1080p and 720p video as well .... ]

What I’m really impresssed with so far are:

1. The new AF tracking system, here is a quote from the Canon website: “As an example, with an EF300mm f/2.8L IS USM lens, the EOS-1D Mark IV can track a subject approaching at 50 kph/31 mph up to about 8 meters/26.2 feet away. This is the same specification as the EOS-1D Mark III. However, with the 39 cross-type AF points, the Mark IV’s subject detection and tracking performance have improved substantially over the EOS-1D Mark III’s. This combination of hardware and software (AI Servo II AF algorithm) improvements enables a more stable AI Servo AF control.”   Which translates to locking and tracking a subject without having to keep the AF point on the subject.   The system will actually track the subject and select the proper AF point as it needs to.
2. Noise Control!  How molly it looks nice at ISO 2000.

Sample movie and images can be found on the Canon Japan site.

For more information please visit the Canon Digital Learning Center.