People assuming that the crack was caused by something done by Ten seem to have forgotten that earlier this season saw the creation of big arsed Fischer Price daleks. My money is on them having something to do with the crack.
The other thing I'm very conscious of is the Doctor's statement "It's all about you" to Amy. I suspect we have some sort of timey-wimey backwards thing reminiscent of Bad Wolf, where Amy does something which causes the crack to leak backwards into her own timeline.
There's also the fact that a 'later' or 'alternate' Doctor appears to be crossing his own timeline to ensure that she remembers things. If Amy's ability to remember people after the crack has touched them is what makes their survival possible, "Remember what I said to you when you were 8" (ie. before we started looking at the crack) might be about the Doctor's very existence.
I strongly suspect Rory will be back, or at the very least reinstated into history/memory. What happens when the crack closes?