America is a huge market (only topped by China) and one thing going for us is patriotism. People love supporting America and everything it stands for. Along with this fact, many of the international companies have their roots in US soil.
I'm just saying that if they start to jump on board with the .US extension then I can easily see it as a clear number 3 extension and I would even go as far as saying it might be more popular than .net.
Give it 5 years though, this kind of thing doesn't happen in a year.