TTT -- if Corbyn does end up winning, and goes on to lead the Labour Party into the election, then it's not entirely impossible that he'll be able to unify most of the Left and in doing so pose a serious threat to the Tories. What seems to be his strong point currently is how much of a fresh face he is. That appeal is unlikely to last very long. But if it does, then the Tories should be careful about their current pointing and laughing.
On the other hand, Corbyn probably won't be attractive enough to the centre of politics to win. But if he's been underestimated as a Labour leadership candidate, it would be dangerous to do the same in the General Elections. We'll see.
Personally I don't think Labour under Corbyn has a cat's chance in hell of winning an election, and I'm sticking to my "I'll vote Tory if he's in charge" line, but certainly the Tories will need to be wary.