re: What would North America be like today had the American Indians been left alone?

In order to answer, we must pretend that Europe was not a contender.

The Spanish explorers looking for Gold; the English and Portugese looking for the NW Pasage and also what is now Capetown; you eliminate these and I believe that Asia and the natives would have discovered one another and had a r'ship very similar to 17th/18th century French-Canadian Mohawks. Of course, France sent expeditions as well, but up until Napoleon, the country was basically a lost cause (losing war in Europe and colonies). North America, even without the French, would have been "conquered" somehow, but maybe not so violently? Also, diseases would have to totally be out of this picture.

I guess, in other words, take out the Scandinavian/Germanic cultures and the Spanish and the entire world would be different -- the natives, Aztecs, Incas, etc. in the 16th century would have all survived. I like to think that the Chinese would have sent explorers to the Americas (again, pretending much of Europe pretty much didn't exist) and struck a very business-like and culture-friendly bit of mutuality. I wonder how Chinese-Native chicks would have looked like?

This is actually a great question. A lot left on the table and who knows how technology would have gone?