If I may throw my own thoughts into the fray in answer to a couple of things:
Our protagonists were supposed to be dream-diving, as in Dreamscape, or Paprika (which director Nolan acknowledged as an inspiration). But dreams don't need VR architects, nor do dreams have faulty details, like the rug in the opening scenes.
To me, it does make some kind of sense. If someone is dreaming on their own, then yes, there's no need for an architect. Get a bunch of different minds together, however, and I can imagine that if the world was left to them, the strongest would win out over the others. The use of the architect is to design a shared dream world. Don't forget that, in the Inception universe, shared dreaming is a military invention used for the training of soldier - they'd have needed a way to be able to control the environments they put the soldiers in.
Inception was also inconsistent. We are told that the Moro reflex, or "startle reflex" is used to wake up a dreamer. The hotel dream world went into freefall because the dreamers one level up were falling off a bridge. So why was the whole elevator stunt necessary? The dreamers falling off the bridge should have been enough to dissolve the hotel dream world. (In other words, it was not the hotel world people that needed to be startled awake.)
This is explained in the film - the sedative used by Yusuf has to be incredibly powerful to allow for the complexity, and depths, of the shared dreams - which implies that the sedative travels down the layers with the dreamers (and, I believe, is backed up with the fact that the time that can be spent at each depth is exponential at an alarming rate - months and years rather than hours and days). The standard "kick", that sense of falling, isn't enough, so they need something stronger, like an explosion taking away the floor, like a lift crashing down and flinging you up, like a van hitting an expanse of water after a high fall. The riding the kick was simply a fancy way of stringing it all together for the sake of drama (and, to some extent, to meet the ten hour deadline).
I watched Inception for the first time yesterday, I'm a tad slow on the uptake generally and this of course was no exception. I struggled to get my head around it from the off, but, realising this film deserved a bit more effort than the standard action pulp I continued watching and after a while it began to make sense(kinda) I'm still a little vague on the "Mal" thread, From what I understand she is truely dead, and only exists in Coobs dream state, created by his unconsious mind out of gilt? and that would explain why she is constantly trying to sabotage Cobb's efforts? Cobb's way of punishing himself, as we discover that he was ultimately responsible for her death?
The one thing I don't understand with the Mal - Cobb thing, is why didn't She/He spin the top to prove they where back in reality? And why did they both use the same Totem?
More or less, yes - Mal was kept 'alive' in Cobb's mind because she starred in a number of his regrets. I think, in the film, it's mentioned that he doesn't want to forget them (which gives us the third meaning to the title - throughout the film, a few characters say to Cobb that he doesn't want to die an old man "filled with regrets" - something that goes all the way down to limbo and comes back up to change him).
We see a scene of Cobb in his shared limbo with Mal, spinning the top and putting it back in the safe to show her that she's in a dream. What he doesn't realise is that this idea rears its head back at the top level and, ultimately, kills her.
As for the totem, I don't think we ever actually see Cobb's original totem. The spinning top is Mal's, which I assume he's using because of the sentimental value.
