A few years ago, the DNC somehow got my name and address. (I'm thinking that a friend of mine probably gave it to them as a joke) They'd always include the survey along with an envelope that was "postage paid" but asked me to actually put a stamp on it to help out the DNC, by saving them the cost of the postage. So I always sealed up the envelope (with nothing in it) and sent it back to them, without placing a stamp on it, naturally. Eventually, I stopped getting mail from them.
I'm always one to do my part, you know. ;)