Like Memento, I think I'd probably need to see it several more times to begin having a real grasp--or as much a grasp as Nolan intends the viewer to have--on it.
Although the top appears to be losing momentum at the end--and it certainly sounds like it's beginning to wobble--the ending, I think, is an inception on the viewer, the idea that what appears to be Cobb returning home to his real kids may really just be another dream. But he doesn't seem to care one way or the other because he never stays around to watch to see it if stops; his kids turn to him, and he runs outside to embrace them.
Reading people's takes on whether the end is a dream or reality, I haven't come across any of the pro-dream theorists noticing some parallels to Memento. In Memento, before Leonard kills Teddy., Teddy explains that Leonard had already killed his wife's attacker. Being that Teddy. isn't the most trustworthy guy, it's hard to accept what he says until it's revealed that Leonard intentionally duped himself into killing Teddy (the most recent of multiple John G.'s) so he could continue on this quest he's created to give his life meaning. When Dom and Ariadne find Mal in the world he and Mal had constructed, she tells him what he believes is reality--the globetrotting, the working for powerbrokers, etc.--isn't. Her explanation may be nothing more than his guilt and subconscious pulling at him, or it could be--if he's still in a dream at the end--that she isn't dead in reality, that she enters his dreams trying to pull him out. She does stab him, after all. Or she could still be a projection of his subconscious but one that's connected to the part of his mind that knows he's dreaming.
Towards the end of Memento, especially during Teddy's revelation to Leonard, Leonard's memories begin shifting between what actually occurred and what his mind has construed: he sees himself in the mental institution instead of Sammy Jankis, he sees himself playfully pinching his wife, but then sees himself giving her an insulin shot. In every flashback to Dom and Mal's dream world, the two of them are young. But when Mal says, "You promised we'd grow old together," Dom says they did, and then there's a cut to a brief scene of them walking hand-in-hand in their dream world, but they're old. This wouldn't seem that odd except in flashback to them killing themselves on the train tracks in order to wake up, they're young and at that point they've lived in the dream world for 50 years. (Someone on imdb said there's a shot of their hands looking old before the train hits them. Did anyone see that?)
As for the "back to reality" interpretation, the fact that Dom wears his wedding ring in dream sequences and doesn't in what's supposed to be reality suggests there is a reality he returns to throughout the film. Also, as many reviewers have noted, it's not coincidental Ellen Page's character is named Ariadne, an allusion to the woman who leads Theseus out of the minotaur's maze. If reality is where Dom winds up at the end of the film, then Ariadne has been the one who has helped him navigate through his deep-seated guilt surrounding Mal. Some reviewers have noted that two sets of children played Dom's kids, which would seem to indicate his return home is a real one since the kids would've aged some since he's left. Also, if the whole movie were a dream--or he's in a dream at the end--at some point he's going to wake up, and not much time would've passed in reality. For it to be otherwise, a whole storyline would have to exist outside the movie--he's in a coma, he's in the Matrix, etc.
I lean towards the reality interpretation, (I think someone could make a strong case for him being in a dream from the basement scene on) but I don't think it's as big an issue for Nolan as it is for the viewer. Leonard, in his few minute segments of full awareness, knowingly perpetuates his quest, embracing what gives him purpose. With Saito's proposal, Dom finally has a means to get back home to his kids. Ultimately, he does that in reality or in a dream level, and his walking away from the top seems to indicate he doesn't care which one it is.
A couple of miscellaneous things I'm hoping you know the answers to:
The conversation between old Saito and Dom is different the second time. Is the second conversation supposed to be the tail end of the one they start at the beginning of the film or has Dom actually been there before?
Did you make out what any of the documents Dom pulls from Saito's safe say? I suspect the only significance is what's blacked out since in the next dream level up Dom says Saito was holding something back from him.
Did you notice if his passport stamp says anything out of the ordinary?
Oh, one last thing. I think it's interesting how even fundamental editing and storytelling techniques add to the film's ambiguity. For example, in an ordinary film, when a character says he's going to, say, catch a flight from Chicago to L.A., and boards the plane in one scene and in the next is somewhere in L.A., the viewer finds nothing strange about not showing the actual flight. But take the end of Inception, for example. In one scene Dom's father-in-law is greeting him at the airport; in the next they're at Dom's house and the kids are playing outside. At least twice in the movie, Dom explains to another character that in dreams you find yourself in the middle of a situation but don't recall how you got there.