I read this in less than 24 hours. It's an excellent sequel to a great premise and, I think probably the best in the series thus far.
The afterword suggests that each book can be read in any order, but frankly, trying to read them in any other order than the one they were written in probably wouldn't work.
Anyway, to the story. It's a post-AI world, and the AIs have just discovered that part of their code includes a shutdown command. They retaliate by initiating an attack against humanity, and in return, America and China unite in shutting down all complex AI within their borders. Sadly this just makes the AI processes which assumed war was coming to speed up. The rest of the story tells the tale off how they plan to work around it.
I'm looking forward to seeing where the author takes this one next.
As an addendum, I got a proper tickle from the fact that in this story future, Cory Doctorow (an exceptionally pro-creative commons author) becomes the head of Disney (an exceptional creator of copyright materials, and the key part of pushing the copyright laws further and further). Nice :)