I, like Len, have and use both Nikons and Leicas. They are very different beasts and both have their place. To me it is never about weight, it is about how I choose to photograph.
I have used both my Leicas and my D800 (as well as my D3) for street photography. I have used both for nature images. I find the images equally wonderful because they suit my mood and method of expression at the time. That is also why I sometimes use my old Polaroids from the 60s to make an image or two.
Too often folks get caught up in debating about equipment. The majority of equipment today is superb and because we are different, we choose different camera systems. If we all chose the same thing life would be too predictable and boring.
Maybe we should just grab a camera and go photograph something.