I own a 5D Mark II and a 7D. I'm really interested in the Mark III since it seems to incorporate features from both the Mark II and 7D in that it' a [relatively] high fps, good autofocus, and a full frame sensor...although it might not be an official merge because 7D shooters probably like the extra reach of the crop sensor and also wouldn't want to sacrifice the 2.5 fps. That being said, I probably won't upgrade immediately because for my work, it's more convenient to have two bodies with separate lenses on than to have just one body and switch lenses...and at the price of $3500, I'd probably have to sell both my cameras to afford this!
The specs look really great though and when I do save up enough, I definitely would like to buy this. I don't understand why there's been so much criticism of the 1DX, and now 5D III, specs because they focus more on ISO than megapixels. Reading this site for years, it seems like the majority of people wanted Canon to focus less on megapixels, and more on ISO and DR...people would often dismiss the 'megapixel myth' and slam marketing departments from selling megapixels instead of focusing more on issues that more directly affect everyday usability (like AF and ISO). I understand some people - like those who do studio work, or wildlife - need many megapixels, but I think many shooters that visit this site (wedding photographers, photojournalists) prefer to be able to pull off a handheld shot in natural light at a higher ISO than to have to rely on a tripod or external flash. Besides, I don't think 20 megapixels is that low ;-)
This is definitely something I'd like to be able to upgrade to...the fact I'm going to hold off is more a reflection of my finances than a lack of enthusiasm!