Anonymous is not into stealing users data. They trend toward pranking, not theft.
My vote is organized crime, like eastern europe or russia.
I don't know how they can "arrest" anyone for "PSN Downtime", since the downtime was entirely caused by lax practices, lack of security and inept IT on Sony's part. If PSN was actually secure - it wouldn't have been hacked... Or more the point, why were they storing important credit card information on a publically connected server that any kiddie scripter can access? All of that stuff should have been kept on an actual secure server that was locked down and not accessible via FTP from the Internet...
Sony has been looking bad for a while now - all the better for XBox 360 sales, not to mention XBox 720 hype... Hey, maybe it is a large, criminous organization with lots of programming talent available, an organization that has already created all kinds of data mining and subversive code, and maybe it is called Microsoft - not to use the credit, but to sell Kinect and XBoxes...