I think the main thing people miss about this movie is that there is no "right" answer to whether the top fell or not at the end. It was left open-ended on purpose. I think the most praise-worthy aspect of the movie was its ability to live up to its name. It infects people who watch it with a bunch of ideas. (Not everyone mind you, at work I overheard somebody saying they had just got back from the movie Interception starring Leonardo DaVinci)
I find it hard to argue that Cobb was actually awake at the end because the layer of reality that the movie tells you is the real world is very dream like by the movies definition of dream like. You never see how characters get from point A to point B. Cobb is being chased by some unknown corporation trying to kill him with no explanation (not unlike Fischer's trained projections.) The characters never have any real interaction with people other than other main characters. There are other things like how does Eames infiltrate Fischer's company in the "real" world? and why is Cobb's homecoming scene _exactly_ like his memory? They never show characters eating or sleeping, etc. The film was put together to be extremely dream-like even in the "real" world.
@Fatecrashers:
1. They were testing the dream technology and were testing setting up dreams inside dreams without sedation. This is supposedly dangerous because the more layers you add the more likely it is that the dreams will collapse and you'll get lost in limbo.
2. Saito didn't kill himself until Cobb found him because he didn't know he was dreaming.
4. The point of them being young the first time they show the train scene and old the second time is because Cobb is coming to term with his relationship with his wife and her death. His projection of Mol accuses him of leaving her saying that they were supposed to grow old together. He, at the end, reasons with her, "We did grow old together." and that's when they show them as being old on the train tracks.
5. I think this is a pretty weak argument. See my reasoning for it being a dream above. Also, I think it's possible that everything Cobb says and believes could be false. It could be that he and Mol were trapped in limbo and he was the one that couldn't realize it was a dream and wake up. So she tried to plant the idea that it was a dream in his head but failed. And to rationalize his wife's "suicide" he misremembers it as having happened the way we saw it in the movie. In this way the Mol projections would represent his subconscious telling him it's all a dream and he needs to wake up. Which explains her motivation. She's not his guilt, she's the virus-like idea that Cobb's world is not real.
@Jackal: As for real life questions, someone I talked about the movie to suggested that movie was an allegory for moving on after a tragedy. Cobb needs to come to terms with the fact that his wife is dead and that a world without her is his reality now and he needs to be happy with it.
@Inceptions version of dream world: I don't think it's far too realistic. Dreams always feel real while we're in them (unless lucid dreaming.) It has some of the important aspects of dreams that I mentioned above. Going from point A to point B but not knowing how, not interacting with things around you other than certain people, etc. Also, the time dilation effect is pretty common in dreams, I think. I've also seen it referenced in movies/books/shows before so I'd assume most people notice it. Also, for anyone looking to get into lucid dreaming and wanting to have a "totem" to help you realize when you're dreaming. Star wearing a watch and looking at it frequently. If you look at it in a dream you may realize you're dreaming when you see that' it's cheesburger o'clock.