I did a bit of googling to find this thread at the movie's site in which some clever people puzzled out precisely what must've happened, and the excellent graphic created by one of them (originally hosted here, but I figured I'd cut his server load a bit). I'm pretty sure he's got it right, or at least got the most reasonable of any self-consistent explanations.
I really should've done more Stats tonight, since I'm now down to doing the project and essay on Wed/Thu/Fri nights. Also, I shouldn't be up this late. Bleh. :-/
At least I don't have to wash my hair tonight, since I went for a wash-and-trim on my way home. (Not that you'd notice, since it was just half an inch to even things and remove split ends.)
ETA: I should note that a) the trailer for Primer kinda sucks; it's misleading about the actual themes, which are largely about how the ability to find out information that somebody else didn't want you to, and either carry or transmit it back to your past self, makes trust impossible; and b) if you didn't like Memento (which played with memory in similar ways to how Primer plays with time) you probably won't like Primer either.