Excellent thoughts.
It is my personal belief that everything we need to accomplish can be done right here in America with a network to Africa and the Carribbean. So I agree with many of Pan's points about establishing economic independence in every area of life; hospitals, utility companies, etc. This really is important for building any type of infrastructure.
I also agree with Om's point about buying land and Riada's point on resolving family conflict.
However, there are still some mindsets that believe that establishing a separate nation is necessary. And I can understand the perspective (even if I don't agree with it entirely), because would it be possible to build infrastructures without absolutely any reliance on non-black sources with the current state of the black economy in America and Africa? Even if we got everything together economically, we still woudl have to contend with the government, which is not directly in our control. And even in Africa there are governments that are either corrupt (as James pointed out) and/or under white or Arab domination in some form. So with a 'new' nation, at least people would get a chance to start fresh; create and control their own laws without outside interference.
It is also important to remember that a 'new' nation would hopefully bring together mindsets that were already 'progressive', and willing to see the importance of uniting regardless of various differences, especially ethnic wise. With other approaches, additional work might have to be done to get rid of biases that could prevent people from building.