Had a chance to play with the new A7r and 35mm f/2.8 Zeiss lens yesterday (I also used it briefly with a Zeiss 50mm f/1.4 for the DSLR mount). It is certainly an amazing package: even more compact than my Leica (although the differences are small, and the Sony lenses are still significantly bigger) and very responsive. I was literally blown away by the number of features on this thing. Having used Leica exclusively for almost two years, it feels odd having dozens on indicators on your LCD-screen, as well as over 20 menu pages. In that respect, it certainly isn't a camera for me. Too many bells and whistles, too many distractions.
It is quite easy to use however, once you get the hang of it. Different dials for shutter speed, aperture, ISO, all on a compact body. Didn't get a chance to look at high ISO results, but I'm sure Gordon will.
The image quality this camera is capable of producing is very impressive though. My friend Gustav, who has the camera on loan from Sony for a couple of days to test it out, had a photo shoot with a model (even though he's known for his wildlife photography). At 100%, it seems like you're looking at the model through a microscope. Wrinkles, facial hair, it's all there. Not sure the model is going to be happy with cameras like this, and it certainly is more sharpness than I need myself, but it is impressive.
You can see some of Gustav's results here: http://www.dyxum.com/dforum/my-first-re ... page1.html
One last thing: the shutter is indeed very loud. If you need a discrete camera like I do, this might not be the best option.
Here's the A7r next to my Leica.