I know your question has already been answered, but I discovered something interesting this weekend while playing through a second time that pertains.

You don't even have to take down all the businesses and rackets or complete all the hits to become Don of NYC. Taking down the compounds was my favorite part of the game so I did that fairly quickly the second time around. I also did the storyline missions pretty much right away so I could keep more money. I didn't do more than 2-3 hits and I still had about 10-12 businesses/rackets/warehouses/hubs left and I was made Don of NYC. I had completely taken out the Tattaglias and Cuneos, but I still had yet to take over all the Stracchi's and Barzini's businesses. So really, if you just want to "beat the game", I wouldn't sweat doing everything; I would worry about the main missions and compounds. It took me 19 hours the second time to become Don.

I would be interested to know just how much you exactly have to accomplish to be Don of NYC. If you just finished the story missions and took over all the compounds, would you still become Don of NYC even if you hadn't taken over any businesses? From all the reviews and comments on the board, I thought you had to accomplish everything that the game had to offer first.