Elon Musk has posted an update on SpaceX: Monster Progress Update (Mostly Falcon 9) - Aug.17.07. The US Air Force has decided not to launch TacSat-1.
This, as Elon Musk puts it, "is not a reflection of the Pentagon's confidence in the Falcon 1". It seems that TacSat-2 , which was launched earlier on, had already tested the technologies that the TacSat-1 was supposed to test.
SpaceX still intends to launch the Falcon 1 next year though; even if it does not have a payload...