When this story first broke, I remember thinking, "I really, really, really hope the shooter wasn't a Muslim."
I think it is clear that, for whatever reason, Hasan was motivated by a Salafi-style ideology. Reports say he shouted "Allahu ackbar" as he shot everyone. I think it's safe to say that he saw his act as a form of jihad.
Obviously there were other factors. I've read reports that he's gotten more and more extreme in his religious beliefs. And he has been discriminated against and been subject to abuse for those beliefs before—which probably further radicalized him. But it's not hard to see how someone with Salafi-style ideology would see the soldiers Hasan killed as part of the "other side." They were, after all, being deployed to places where they would probably end up killing Muslims.
All in all, though, I'm hopeful in the way that America and the Muslim community has responded to this. The army chief of staff is warning everyone not to judge all Muslims or Muslim soldiers by this guy's actions, and even Republican senators are saying that his actions don't reflect on Islam as a whole:
http://www.nytimes.com/2009/11/09/us/politics/09casey.html?hp
(The exception, unfortunately, is Joe Lieberman, one of the biggest scumbags in the U.S...)
Reading this thread, and your guys' response, also makes me pretty hopeful. Let's hope everyone keeps a cool head.