I don't buy it. This isn't Anonymous' style at all. Say what you will about their methods, but it all serves a purpose. Everything they do is free speech and freedom of information. Taking down Facebook doesn't help that goal in anyway shape or form. Also, November 5th? A group as big as Anonymous wouldn't need anywhere near that much prep time.
Worst case scenario, Facebook is DDoS'ed for a day, tops.
Worst case scenario, Facebook is DDoS'ed for a day, tops.