They can do something HBGary-style and hack sony's servers to gather confidential information that would embarass the company and bring the stock price down. That would hit where it hurts, can be doable with some social engineering, and any company that big is bound to have some skeletons in its closet.

Not that I condone these actions, I'm just pointing out that they have done finer things in the past than just using LOIC.