Summary: This is a professional level DSLR. For sports and wildlife at 10fps and a crop factor of 1.3 it just doesn't get better than this. If you are lucky enough to find one, go for it, you will never regret it.
My experience with the Mark IV that I purchased has been satisfactory!
10 December 2012
Summary: I own two Mark 111s. I wanted the Mark IV for the video and the enhanced pixels. I chose to go the Mark IV route because I continue to want the magnification factor--as I am primarily a bird photographer/wildlife photographer. I purchased a camera body that showed several blemioshes. The seller reported the camera functioned as intended. I have had the camera for a short period of time--and it does function as intended.
It is a (5) Star Value if you can find one in mint condition.
10 October 2012
Summary: I have owned a 1D Mark III for many years and I wanted to upgrade to higher level without giving up the 1.3X crop factor. The 1D Mark IV was the ideal choice. I purchased the Mark IV from KEH on eBay, and the product was exactly as they described. The Mark IV is a very good combination of mega-pixels, low noise, fast and accurate auto focus and added features.
Summary: Canon EOS 1D Mark IV 16 Megapixels The 16MP, $4,800 Canon EOS1D Mark IV is the first and only APS-sensor camera to claim a maximum ISO of 102,400, and has a recommended top ISO of 1320. It has a signal to noise ratio of 41.4 dB at ISO 100, and doesn't dip below 30 dB until after ISO 1600. Digital noise is effectively suppressed up to ISO 1600, although overall image quality deteriorates rapidly by the time you reach ISO 12,800. Still, an amazing performance.
Summary: *** UPDATE, 2/21/2012: I sold my 7D bodies to upgrade to another Mark IV. The 7D is great, but the Mark IV is vastly superior on nearly all fronts. *** Just like with the Canon EOS 7D, Canon took a serious look at their line-up and listened closely to their customers as well as market trends. I'd have to say they have come out with an excellent camera that is extremely versatile.
Summary: really good DSLR with an incredible sensor (SPECS seem rahter low, but it's not always quantity, but also quality of pixels) I like it for it's incredible autofocus capabilities, its possibility to shoot on 2 cards, limiting possibilities of ISO, Time and Aperture Range, etc. simply an incredible workhorse. BTW, 12800 ISO produces usable image results!