Yes I agree with I took the red pill, I think the spinning top isnt just 'tacked on' for a cheap 'woah' as Raistlin says. Nolan very deliberately and skillfully balanced both possibile ending interpretations (dream or real, there are more than two but those are the main obvious ones) precisely so that neither ending has any more probability over the other

ALso I hate to quote myself but I really want to discuss:
Quote Originally Posted by Blackmage_nuke
How and why did Cobb and Mal go into the first limbo? What were they doing at the time? It only shows them waking up on the floor, there is no one else around that they were trying to extract information from and no one to operate the machine. If there isnt an answer it begs the golden question presented in the film "How did they get there". This seems to support the "the entire movie is a dream" theory
Infact I cant think of anything that describes the past of Cobb or anyone elses for that matter besides Fisher (the photo with the pinwheel) before Cobb's first time in limbo.