Get rid of the "Report" link under comments and posts. Some possibilities, in decreasing order of preference:

• Just remove it completely, and handle spam and other crap by giving the moderators a page where they can easily see the recent comments that got a lot of downvotes (if they don't already have one)

• Rename it "Flag" so it doesn't get confused with "Reply" (I bet that happens more often than people reporting spam)

• Remove it for any post or comment older than a day, or for any post/comment that has positive karma.

• Give users an option in their preferences (on by default) to hide the link.