Like when they modified the Times most influential person ranking, it was just a lot of people running an auto-voter on their machine.
As an example, the anti-Scientology protests were reported under the catch-all banner of Anonymous, but the people organizing it and hitting the streets were also from rival forums such as Something Awful. Funny enough, the protest movement is completely different from (and at odds with) the original catalyst: other Anons DDoSing Scientology websites for using the DMCA to take down a video on YouTube. As someone mentioned earlier in the comments, one core motivation is trolling, or "lulz," so under this so-large-its-useless umbrella term "Anonymous," there are groups sabotaging one another just because it's funny.
The core people
organizing* these DDoS attacks come and go, but they are a dedicated few who have the time and skills to design such programs to distribute to the masses. As in the Time magazine hack, it was respectably sophisticated (this article does it justice: http://musicmachinery.com/2009/04/15/inside-the-precision-ha...). And yes, this core group does have botnets, as well as excellent social engineering skills to motivate *channers to download and execute their software.I love watching people and organizations of all varieties underestimate just how tenaciously annoying they can be.
A 4chan poster can't do the same thing. He's attacking from his own computer. Either he attacks through tor (slow) or he doesn't (unsafe). Hence why I thought the post above does not make sense for anon's case: he can't hide his traces without channelling the attack through Tor itself.
