It's never a good idea to respond to rejections. By all means whip off a page of scathing comment if you've had one that you feel totally misses the point or that's full of spelling mistakes, but don't send it. I repeat: DON'T SEND IT! Of course, if you really think the editor's an uneducated moron you aren't going to submit anything else to them, so it won't matter–or will it? You have no way of knowing where that editor might move to in the future, or who they might tell now. You absolutely do not want to get a reputation for being rude. The chances are that once you calm down you might find some justification for their comments. If the editor's missed the point, could it be because of the way it was written? Everyone has their critics, and arguing with them really is pointless.
    When you don't get a reply to your submission, by all means wait until the stated response time has elapsed, then query whether your work's still under consideration, but don't complain. You may receive a standard rejection, which is frustrating, as you have no way of knowing why your work was spurned, but don't be tempted to write to the editor for an explanation. The reason editor's use standard rejections is because they're too busy to go into details on each individual submission. Often there really is nothing to say other than that they already have enough stories, poems or whatever, or they simply liked another one better.
    Not all rejections are like used tissues. Sometimes they come with positive comments and constructive criticism. They're still disappointing–so near, and yet so far–but at least you know you got close, and you have some pointers on how to get that step further. That must be worth a thank-you note, surely? NO! As I've already said, editors are busy, so the chances are they'll have forgotten about your submission already. Do you really want to remind them about work they've turned down? It might seem impolite not to reply, but if you do, you'll make yourself look like an amateur.
    When it comes to rejections, the least said the better.