His video seems to indicate that he is (or was) a soldier at a military base in the area, and he seems upset that the Army gave him a "mini-Bible" before some tests at some Army base in Phoenix he calls MEPS (which would be the Military Entrance Processing Command). This makes the claim in this news report that it was an automatic weapon a bit unnerving. (Of course, a lot of these early accounts turn out to be wrong.) This CNN report says a Glock 9mm pistol--a lot more likely.
UPDATE: This Fox News account reports:
According to the law enforcement official, the suspect began shouting something before shooting wildly with an automatic weapon. Shots then rang out from the crowd -- a security agent or someone else fired at the suspect who survived.Being Arizona, it could have been one of the many armed civilians, too. It is unclear now if this helped or hurt, although it does not appear that the shooter was hit.
UPDATE 2: Jim Lindgren over at Volokh Conspiracy points out that it looks like a mental illness problem--and his politics are not likely significant factors. But so what? What little evidence is available comes from someone who purports to have gone to school with him, and describes Loughner as a left-wing radical. It does seem unlikely, however, that a left-wing radical is following Sarah Palin's site. Oh yes, a pothead--and now, apparently, mentally ill (my guess: paranoid schizophrenic). Wait--didn't I read something somewhere about the connection between marijuana use and mental illness--specifically schizophrenia?
UPDATE 3: Early reports about being in the Army seem to be wrong--the Army apparently rejected him in 2008. This account confirms a history of violent threats, and behavior that fits the mental illness explanation. Also, some drug charges several years back that confirm the friend's description of him as a pothead.