It would be pretty nice to know who upvoted your question or answer. And sometimes who downvoted to ask the person who downvoted why they did it. Some people downvote for no reason at all and it would be nice to find out who downvoted.
This has been suggested once before and was given the following reasons as to why it was not approved:
Pokemaster (Super Admin) can see who upvoted / downvoted a post. But the reason ever other user type can't is merely to spare all the arguments it would cause.
If you could see who downvoted you then people who take points way too seriously would start a vendetta on that person who downvoted which in-turn is going to lead to them getting in trouble with the moderators.