I was getting the impression all over the place that she made a conscious choice to leave, cut out her own grace, and because of that she fell. She wasn't thrown out, she threw herself out.
I'm having difficulty with the logic of Anna's actions, which is really the show logic on angels. I'm okay with hand-waving it but I need to spit out what bugs me about it. If Angels have to be obedient and follow orders, then how is it that they have the free will to Fall? If they can choose to Fall, why can't they choose to disobey orders?
I suppose you could answer that in the Angel form they have tremendous pressure on them to be obedient, and the only way to shake that is to Fall, but then it becomes a matter of degree not ability. On the other hand, I think we have the same issue with Ruby - demons have tremendous pressure on them to be evil, and she's resistant to the pressure and choosing to act good. But Ruby retains her demon powers, and Anna had to abandon her Grace. Now that she's reclaimed it, she can no longer exercise that free will. Hmmm. Okay back to hand waving.
Sam's Plan: This is also bugging me a bit. I see how Sam could dispatch Ruby to summon and trick Alistor, but how did Sam know that Dean would be contacted by Uriel (at least in time to arrange for the showdown)? Unless I'm misremembering, Ruby summoned Alistor before Dean had his dream. Unless Show arranged those scenes out of sequence, which would not, in my opinion, be playing fair in the game of misdirect.
Heh, other than these things, I really, really liked this episode. For awhile it's been bugging me what could have happened to Dean that he'd come out of Hell all happy-go-lucky (in a sense) yet have just endured 40 years of horrific torture. Now it makes sense - he was tortured for 30 years, but the last 10 years he was the torturer. So while he carries the trauma of the 30 years of torture, he really emerges with fresher emotional scars of tremendous guilt - which would be consistent with his immediate behavior, and his reluctance to discuss the events. The writers really knocked this one out of the park.
Castiel is awesome, and I've developed a total man crush on Misha - that guy can ACT. If he Falls though, wouldn't he need a new meatsuit? I hope not.