I have made a blacklist of known griefers that can help server administrators when it comes to griefed servers. You can contribute to it by adding the ip(s) of the griefer, the username(s) used.
http://xboard-project.info/blacklist/
Please give as much information as you can on it, screenshots and debug logs. But please don't paste the debug logs in the notes/more info area. Use http://pastebin.com instead for that.
I will remove entries to the blacklist if they do not contain a screenshot in the Notes/More info area.