I'd have guessed it'd be well into the thousands by now...
No, this wasn't the first one. There were two threads already up by the time I hit the Post button on this one:
http://www.freerepublic.com/focus/f-news/520255/posts
http://www.freerepublic.com/focus/f-news/520260/posts
And then there must have been a thousand threads started after that, all throughout the day. You can do an archive search on "World Trade Center" (with "match all words"), to see some of them.