Having just seen it and not having read any of the rest of this thread... here's my take (sorry if it's repeating things that have already been stated)...
It's ALL a dream. Cobb is nuts / a vegetable. There's no such thing as being able to go into peoples' heads via some sort of dream technology. It's Cobb's brain's explanation for his physical state of being. His wife as "the villain" is his subconscious' way of trying to make him wake up, but his brain won't allow it for some reason. his wife is living in the 'real' world with the real kids, watching over Cobb's comatose body somewhere, not able to wake him up.
Even if that's not a "correct" viewing of it, and there's some "reality" to the whole dream extraction/inception thing, the ending was DEFINITELY a dream... I mean, what are the odds that his kids would look exactly the same and be wearing the same clothes as the day he left them?
Regardless, the movie's awesome! Loved the soundtrack, and I love that there's no answer and that he could make it as ridiculous as he wanted and it wouldn't matter... because there's no answer. 9/10