I think that in a couple of years this will become the accepted reading of the film, and differing interpretations will have to be skillfully argued to be even remotely considered. The film makes this clear, and it never holds back the truth from audiences. Some find this idea to be narratively repugnant
The above is an excerpt from a discussion of the film's themes, and will completely give it away, so don't read it if you haven't seen the movie yet (link to full review at the bottom).
We had a similar discussion to this on the way back from the movie, which we thoroughly enjoyed. Otherwise, a good summary of the themes in the movie. Well worth your money to see in the theater; it was the first movie we'd gone to theaters to see in over a year and, despite every reason for why we don't go to the theater anymore sitting or occurring in our theater, we enjoyed the hell out of Inception.
On a side note, the review of Inception by Rex Reed led me to the conclusion that he's just become a professional troll recently. Yeah, I linked to it, but damn, if you have to resort to middle-school name calling or vibrator jokes when reviewing a movie with lesbian lead characters (seriously, in the first paragraph?), you've abdicated your Reviewer hat for page views as a Troll. How the mighty have fallen.
Anyway, check out the full Inception explanation (you too, Rex; obviously you need to have it explained to you) at chud.com.