I personally think down voting is not very useful, and should be replaced with a report abuse option.
(Please see update at bottom for change to feature request based on feedback. Leaving details in tack for historical purposes.)
- In real life voting you cannot down vote a proposition or politician no matter how much you would like too.
- It is to easy for people with a high reputation to abuse by down voting people who are just trying to help instead of only down voting the true individuals who are just initially be lame or idiotic. I feel that if someone is trying to help but there answer or question is not well formed or right or inline with the site we should comment and let them know and and help them if possible. They can then update the answer or question or just delete it.
- Stats provided to me by Robert Cartaino (shown below) I feel show that down voting is hardly even used and while not being abused on any wide scale it does get seriously abused by a small few. I feel that if it isn't really getting used much then it should go as it it tends to get miss-used more than properly used.
I think the down vote should be replaced with a Report Abuse system.
How Report Abuse Would Work
This would provide a "Report Abuse" link on all questions, answers and comments. A single report would could be queue as low priority for the moderators to review. However as it gets more and more reports by other individuals its priority for review goes up. It could even have a threshold that would automatically deactivate or remove the report item if gets a specific (large) number of reports. The number of abuse reports can be shown as a counter on the item if it gets more than 1 report. The report must provide an shoot intelligent reason why it is an abuse.
Help Others With Conversation Not Negative Reputation
I am for people be made aware of being incorrect and being helped to be better in the future or correct there post. I am not for maligning another persons reputation with negative values who is just trying to be helpful or earnestly looking for help, even if they where not perfect in the question or answer.
Down-voting is statistically very rare. The account for only 0.8% of all the votes cast on the system. And we're not seeing any large patterns of abuse. Of the 7.5 million users who come to Stack Overflow every month, only 18(!) users have cast more down-votes than up-votes (with > 100 down-votes)... ever! - Robert Cartaino (via email)
While I am quoting stats provided by Robert, I am not implying that he is in favor of this feature. In fact my impression is he is not sold on the idea so he suggested putting it to the community as a feature request.
EDIT - UPDATE 7-9-2010
Since there is already an abuse system it is just called "Flag" which is not a good user experience as it is not obvious what that is for. I would suggestion Flag be called "Report" to clarity.
Also if we keep the down voting why not then make minor changes to it which would be Down Votes require a comment explaining why or you can't do it. This makes it not anonymous, which will make people think before doing it and reduce the abuse even more if they have to explain why it is not a good answer or question. Doing this would make it easier to understand why you got a down vote, because getting one or more with out a reason is confusing.