Ok, so if you hark back to the ending, you'll remember Cobb was reunited with his children and father (Caine) in a sob-alicious final scene. As his usual style dictates, he spins the silver top to double-check he's back in reality, but doesn't care enough to watch whether it ever stops spinning (thus, representing he's in real life).

Caine let slip with the spoiler-goods when he appeared on BBC Radio to promote his autobiography. This is what he had to say about director Christopher Nolan's ending:

"[The spinning top] drops at the end, that's when I come back on. If I'm there it's real, because I'm never in the dream. I'm the guy who invented the dream."

There you have it, final confirmation the ending was exactly what you suspected. I still maintain my stance that Nolan should've done a Ridley Scott and filmed several different endings to puzzle us with—or that Caine's character should've placed his hand on the spinning top, breaking the motion himself and denying us the chance to see it wobbling slightly. Also, he should've kept his piehole trap-door shut too. [BBC via ScreenRant]

Point 2 and 3 make no sense, of course they dont talk to each other, they are meant to be a group of strangers on a plane that have just been in another passengers dream, who is aware of that type of work as he has a militarised subconscience. If he realises they all know each other and he recognises them from his dream Inception will not work surely, so pounding beers and giving high fives around the baggage area is going to fuck things up royal! And he speaks to the border guard.

Point 6, Grandma is out of shot, in the kitchen perhaps making a tasty sandwich for her grandchildren.

Point 7, upon taking and subsequent completion of job his new 'boss' Saito says he would square everything or he can take his chances with his company. And even if they were not aware of his change of circumstances they would not search for him at home as they would still think he is living in exile away from the States.

Point 8, the kids are older and wearing different clothes.

At the end of the day its all open to interpretation but if you listen to the sound of the totem at the end of the film it sounds as if its just about to fall, then the screen goes dark, so what does that mean?

Also with the nature of the films Limbo, its filled with the subconcious of the last person who was there in the shared dream, and thats his dream world with Mal where they spent a life time building that city, so how could he radically change it so quickly and with such detail? And before you mention that time moves slower, he went to find Saito who was there for 90 years(?) to get him to wake and honour the arrangement and then they are back on the plane so when could the re-building have happened? And we can remember seeing him get on the plane so its not one of those "do you remember how you got here" moments of the film. Its possible as a dream he can control it but where to put Saito in this? And if Saito was conscious in the baggage area within the context of a dream surely he would be freaked out going from being an old man to young again and start voicing this concern?

Is he dreaming? I dont know, but some of your points I dont believe indicate that he is.

Happy Holidays!