I don't expect to buy a M9 until the price comes way down. I have two M8's and some beautiful M lenses that I currently use on a M4/3 camera with adapter. The D5100 is superior to the M8 and I expect about the same as the M9. While the Leica lenses are extremely good and are designed to be extremely sharp wide open and very distortion free, the Nikon system is much more versatile and easier to get perfect, in focus photos.
What I really enjoy is using camera bodies like the D5100 and D3200 which can actually look as good or out-resolve cameras like the D800. I don't care about features or built in meters or movies. These little cameras are amazing. And so are the photos they produce.