My feelings are decidedly mixed with the D800's video modes. Some shots are truly impressive, but I don't feel there's a consistency that will be reliable enough for me to use the camera seriously, even with its 'uncompressed HDMI out.' The primary problem is the colored rainbows that pop up unexpectedly and everywhere in the footage. Bypassing internal compression isn't going to remedy this. If you're poor at keeping focus maybe this isn't a problem.
Also, the field cadence of the camera when set to output 1080i is a mystery to me. Yesterday I tested with the Blackmagic Decklink card and the D800 set to 'AUTO' for a 24p 1080 output. Today I'm on the AJA IOHD which doesn't accept 1080 24p signals via HDMI in. "No biggie," think I to myself, "I'll just remove pulldown later." But oh no I won't, the field cadence is bizarro--four interlaced fields and a fifth repeated progressive frame.
Further testing to be done with no memory card present in camera. Jon Thorn from AJA did initial testing with a D4, no memory cards present and an update KiPro Mini, and got the two devices to communicate fine.