I think something should be done with the homework questions: there are too many of them now. I suggest that one reason for closing should be "homework". If at least 3 people vote for that reason to close, the question should be deleted immediately. I suggest to have also a visible sign on the front page for newcomers (right before they register) that this site is not for homework questions.
Let me make a suggestion which seems obvious to me: You should only vote to close a question as homework if you can solve it. By this I mean you have actually thought through most of a solution, not that you think "oh yeah, I could probably do that." Both here and on math.SE, I frequently see questions attract closed votes because they are formatted like homework questions, but they are actually substantially harder.
There's now a custom close reason saying that homework is off-topic.
Something half-way to what Mark proposes for the automatic deletion would be to waive the "wait period" between closure and when people can vote to delete for questions closed as homework. I'm not sure if that's possible to implement but it's something to consider.