I don't think negative rep is a good idea though. That would cause more drama than anything, and people should be clicking the report button not a "minus rep" button.
Although I agree in some cases drama could be generated by someone giving someone else negative rep, the idea that there is positive and negative reinforcement or consequences to how people behave on the forum, and it translates to how the community or peers perceive that person is kind of the point. This will again make a user think twice before posting up something that is not constructive especially if they are worried they will be perceived badly by others viewing their rep. Humans in the end are social animals regardless of how "real" the rep reporting works it is still something that will hit close to home especially to the younger kids that see public perception as everything, especially in the this community lol.
I am a member on other forums and have seen the positive/negative reputation system in practice on other sites using vbulletin and I can tell you that for every instance of drama that is generated there are literally thousands of other instances where the system is a overall good for the community. The rep system offers something that would be difficult otherwise to do, allowing the community to police themselves through peer review. I agree that a report button should still be available as it is on other sites to get mods involved if something needs to be reported, however the rep system is more than just a reporting mechanism for questionable posts, it is a community tool that will help to support better behavior overall on forums and
most importantly support and encourage members to post up more constructive information which other members will value and appreciate and in return reward and recognize. The system will inspire creative competition from the productive members of the community and at the same time help to convince those that may not be so constructive to get involved as they see a direct cause and effect to their actions on the forum through positive reinforcement.
One thing I should point out is there is a difference between the rep system I'm describing and the "like" system already in place. Some differences:
1. Graphical representation of rep (think about how rep works in WoW usually numbers aren't shown instead its a bar made up of little bars indicating a number perhaps 1 rep bar would be 50 rep points, etc.)
2. When you mouse over the bar it shows messaging describing the individuals rep rank or how close they are to getting another bar of rep.
3. A user starts out with a gray bar (neutral) but can go red if rep is below zero otherwise little green bars start to be added based on rep points achieved.
4. Perhaps ranks could be added that give rewards such as access to otherwise restricted forum capabilities, I can go into these in more detail if this system gets seriously considered.
Here is an example screenshot so you can see an visual of a rep system in practice:
