There is a HUGE problem with the top though.
In the earlier parts, it is explained that a totem should be unique to the individual to know whether or not you're in reality. The top is NOT his. It's his wife's original totem which she locked away when in the dream world. Thus, this totem should be void in the first place. Wasn't it also explained that for the wife, it was supposed to spin forever when in a dream?
Also, I don't fully recall, but how many times does the top actually fall? We see the top being swooped up a lot, but how many times does it actually fall. (Quite a few times it's just sitting somewhere, we don't see it fall)
Also, does anyone else realize that all the individuals we see with a totem, they're all connected to some type of "game"? There's quite a few individuals without a totem either.
I got my second viewing today and kept in mind things about the totem; so for what it's worth I think that the totem is valid as the only other person who knows the totem is Mol and she's dead which could make it difficult for her to trick Cobb. However going through the film the second time I actually think it's his children's faces that are his true totem as he never sees their faces when he brings them into a dream and no-one but Caine's character would know what they look like.
We see the top tumble twice; we also
don't see it tumble twice; first when Saito interrupts Cobb after Page's character jumps into his dream and the second time is at the very very end, but it wobbles where as the dream top keeps perfectly straight.
I think the three totems we see (the top, dice and chess piece) are game related as it's very easy to get a hold of a game piece no matter where in the world you are and they have the added bonus of being cheap. The other characters would have totems it's just that the audience doesn't get to see them as it doesn't add to the plot.