It's been viewed that many times because it was linked to by several different news and opinion websites.
I remember sitting on the couch at my friends' house on 9/11 and remembering the thread. I burst into tears for the third time that day (1st when I saw what happened, 2nd when I realized my sister was too close to WTC for comfort) and told my friends what we had discussed. I was convinced the FBI was going to come banging down my door for participating in such a discussion.
-90 was apparently contacted; I wasn't. I doubt anyone else was.