I searched for those tweets mentioned in the Techcrunch article (first from GoDaddy and first from AnonymousOwn3r on this topic) and the time stamps are:
* GoDaddy: 10:35 AM - 10 Sep 12
* AnonymousOwn3r: 11:57 AM - 10 Sep 12
So, AnonymousOwn3r does not seem to have announced the attack before it happened.
