After wondering if I'd ever consider buying a Nikon camera again, along comes this.
Metal body, weatherproofing, compatibility with older lenses (though not all), 16MP > 46MB files, optional battery grip, full 1080 HD video recording with continuous AF.
Ticks a few boxes there.
Certainly moves things forward somewhat for Nikon and gives it something that can do (almost) what a Canon 7D can do in terms of resolution and something it can't which is AF in video recording. As someone who uses old Nikon lenses the compatibility is welcome.
The big question for me and others will be, what is the high ISO performance like? Canon have set the standard very high with the 7D / 550D and it will be interesting to see what Nikon can come up with.
Obviously aimed directly at the "Semi-professional / Enthusiast" market. (God I hate those terms) it now has a higher pixel count than any other camera in the Nikon range other than the D3X. Where this leaves the D300 etc. who knows.
There was an idea that once full-frame appeared, that could be the end of the APS-C sensor. However that certainly isn't the case. In fact it seems to be thriving. In terms of a slight depth-of-field advantage and telephoto reach, these sensors have distinct advantages. Particularly when ongoing R & D manages to squeeze more and more out of them in terms of performance. Certainly the 7D / 550D sensor is excellent and unless you want the very best high ISO performance that you can get, perfectly adequate for most of us, including myself. Also when you think of what has been achieved since these sensors appeared. I used a Fuji S2 Pro in 2003 and when I stand one of those images up against a 7D shot, the improvement is obvious and dramatic.
I do use full-frame, with the Leica M9, and enjoy it very much. It is after all, what I grew up with photographically. However in many ways I preferred the M8 1.3x crop, which removed some of the wide-angle lens problems.