I am not going to regurgitate the specs of this just announced camera (as of 20 October 2009), those you can find it here as well as many other places that you can find using Google.

Here are my observations on the camera based on what little time I spent with it (an hour plus):

1. It looks and feels exactly like a 1D3 or 1Ds3 – which is just fine IMHO as this is a professional tool meant to get the job done, no complaints about the weight or size as it SHOULD balance quite nicely just like its older brothers
2. LCD looks great and works fine indoors and even beside a glaring window
3. No change of controls or menu layout compared to 1D3 or 1Ds3 but with new features added
4. AF locks fast and sure, even indoors lit with weak / romantic ballroom lighting
5. Image Quality very good at high ISOs, colors remain accurate and vivid even at 5-digit ISOs
   

All the comments above were based on mounting a EF 100mm f/2.8L Hybrid IS on the pre-production 1D Mark IV body.

Some additional comments on some other equipment I tested today :

1. EF 100mm f/2.8L Hybrid IS – built like a tank, sharp as anything, good for portraits, very nice bokeh yet retains very high level of detail, weather-sealed and the Hybrid IS does work as good if not better than conventional IS
2. EF-S 15-85 f/3.5-f/5.6 IS – very well built for a non-L, feels good in the hand, wide and short barrel makes for good ergonomics  but yet easy to store, doesn’t seem to exhibit any zoom creep at all, excellent image quality, looks like a very good EF-S lens in the making