Just a couple observations on some of the posts I read.
Host, I don't trust a map that marks DC, but can't put it anywhere near where it really is
Pan, that was basically how this nation started. Under the Articles of Confederation each state was essentially it's own nation, allied with the others for common defense and foreign affairs. That failed, so the leaders created the Constitution.
Now, those were different times, so with the way the economies work now that may be a somewhat viable outcome, but I can't see it working.
Bingle, it's very simple. If a state were to seceed, it would be invaded and brought back into the US unless it could fight off the US military. A state like Maine wouldn't be particularly hard to bring back, unless it joined with Canada or something like in Halx's map.