What means do users have to report plagiarism or posting of copyrighted work?
A button to flag content as plagiarism would be useful. It's not quite "offensive," and should probably have a different effect on reputation.
I've noticed users posting large paragraphs copied verbatim from elsewhere on the Internet.
Worse, these answers often get many upvotes (it's generally good content, just not original). This encourages this behavior and is unfair to users who respect copyright and only post original material.
You could leave comments addressing these issues to the people posting these swathes, but comments don't change the fact that the site still contains the plagiarized material, so it's still in violation of copyright. I've commented on several posts that were blatantly stolen from copyrighted material, and nothing was changed.
Legally (well, technically at least, IANAL) Stack Exchange must remove the offending material as soon as they are made aware the content is infringing, even before the copyright holder is aware their copyright has been violated. Once the copyright holder is aware, Stack Exchange could be subject to lawsuits or DMCA takedown notices. Despite the cc-wiki license, SE could be found responsible if they were aware and did not take appropriate action to remove said content. Since they do not own the content, all redistributed copies (torrents of content dumps) must also be removed. Big headaches for all.
Wouldn't it be better if users could flag copyrighted content, provide a link to the (original) source, and mark it for removal? It would use a similar quorum process as deleting other content.
This would help ensure the content found on Stack Exchange is original, is protected and covered by the cc-wiki license as intended. Simply having an easy way to flag content and a clear policy would go a long way.