I think we down vote too often here. SE has some reasonable guidelines about when to down vote.
Use your downvotes whenever you encounter an egregiously sloppy, no-effort-expended post, or an answer that is clearly and perhaps dangerously incorrect.
Our answers and questions often are a little on the subjective side, but nowhere in the guidelines does it suggest down voting just because you disagree (which I think is why many down votes get cast).
I would really like to see more explanations as to why things are getting down voted. This would allow people to fix the problems instead of just slapping them in the face. I understand this will make the down vote not anonymous, but I think it is a nicer way to go.
I see this as more of a problem when down voting answers. I can provide examples from my own answers which have received down votes. I am using my own answers since I can easily find ones with down votes and not because I need justification or want the down votes reversed.
I also have a question with what seems a spurious down vote:
Again, I am not complaining about these down votes, it is the fact that it happens to new people also.