My rather banal thoughts on the ethics of downloading music illegally are interesting to me because the wrongness of downloading like this seems quite different from the wrongness of stealing (since the loss involved is merely potential and, in fact, unlikely--i.e. most people who download illegally would not otherwise buy that music, I suspect) and because I think I actually changed my mind in the course of writing the post.
Anyway, the question of depriving others of potential future goods reminds me of Don Marquis' argument against abortion. (Is that an illegal link?) Marquis argues that what makes killing people wrong, when it is wrong, is that it deprives them of the future good experiences that they would otherwise have enjoyed. Since abortion does this, it is immoral.
Some people object, though, that this suggests that killing a young, healthy, good-looking, rich person (who is, because of these features, likely to have lots of good experiences in the future) is worse than killing an old, handicapped, ugly, poor person. In certain philosophical moods that might sound plausible, but it's actually (I think) not just wrong but monstrous. Raskolnikov's crime isn't "not that bad really."
Another thing worth bearing in mind is that not all killing is wrong. Killing in self-defense, for instance, can be OK. It is only unjust, unfair, or unreasonable killing that is wrong. Judith Thomson has argued quite persuasively that abortion is not unjust. I'm not sure whether it makes sense to talk about being unfair to a being that is incapable of intentional action, as a fetus seems to be. Abortion could still be unreasonable, though, for instance if it is, in Thomson's words, callous, self-centered, or indecent. This is not the kind of consideration that Marquis deals with, but I think it should be the focus of debates about the ethics of abortion. Or at least more of a focus than it usually is.