The Egyptian military overthrew the government, as they are prone to do. The difference this time is that they overthrew the first and only elected government that Egypt has ever had. And that makes all the difference.
U.S. law requires us to stop giving aid to countries if the government is overthrown by a military coup. The Obama administration has been dancing around describing what the Egyptian military did as a 'coup' to avoid having to face this consequence. The president is afraid that we will lose crucial leverage with the government there is we stop sending them a billion dollars a year. And the president is right to worry - keeping Egypt as a peaceful neighbor to Israel is critical to our interests and the larger interests of peace.
I also believe the sketchy reports that the Saudi government colluded with the Egyptian military. The Saudi monarchy has benefited, in a perverse way, from the seeming antipathy between Islamist government and democracy. If the Arab Spring succeeds in creating an elected Islamist government, then the Saudi absolute rulers would reasonably fear that the Arabs in Arabia would demand the chance to do the same.
Nonetheless, democracy serves peace and order better than even useful dictatorships do. That means America's real interests are in promoting elected governments, even if the parties elected are not as compliant as the dictators they replaced.
The United States should oppose the coup and support the restoration of democracy in Egypt, warts and all.