Fill in for the non 4chan people on this forum.
Over 9000 is a line from Dragonball Z
Used by nerds and similar "omg you have over 9000 powers" etc...
recently /b/ on 4chan has really been kicking up the phrase, going so far to autochange the word "two" to "over 9000" (quite funny when a guy is talking about his computer set up with "over 9000" monitors.
As we all know, /b/ is the internet hate machine. One guy decided to fuck around with Oprah's website when he saw the stuff about paedophiles, and wrote in the first thing he though of with "over 9000" in it.
She read it, thinking it was serious. Now...... we laugh.
Edit: anyone looking for /b/ go here,
http://img.4chan.org/b/imgboard.html. Be warned though, it is VERY NSFW. Much porn, gore and disturbing things... you need a tough stomach.