At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
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When you file an abuse report a few things happen. First, all of the moderators currently logged into the site get a notification (it looks a lot like the "new fan" notification except with a red thumbs down instead of a blue thumbs up). Second, an email blast is sent to all of the moderators about the new abuse report complete with a list of recent abuse reports for that user and whatnot.
The only way that the user finds out that they were found because you reported abuse is if you tell them. We don't disclose the identity of those who file abuse reports on other users. (Unless they're trying to be funny by filing false abuse reports on us moderators. In which case we call them out for laughs. :P)