It's fairly common for companies to put a clause into their terms of service which prohibits the right of the end user to participate in class-action lawsuits. I'm pretty sure both Apple and Microsoft have clauses like this in their terms of service, and from September this year, so did Sony. One PSN user felt that this was a terrible thing to force onto their users and so has taken it upon himself to sue Sony on behalf of all PSN users who were members from before September this year.
The lawsuit, according to documents obtained by Gamespot, claims that Sony placed us all into a position in which we had to choose between our right to a class-action lawsuit or our ability to play online. It also says that although Sony gave users the option of opting-out of losing their right to a class-action lawsuit, you needed to contact the company in writing within 30 days. This is on top of the fact that this whole part of the terms of service was buried at the bottom of the terms of service, a document most normal people wouldn't even bother to glimpse at.
It's not a great thing that companies do this but, ultimately, this is to protect their business from the sort of ridiculous things that happen when stupid people get a bee in their bonnet. It's not to destroy the rights of the user, most of whom would never consider suing Sony.
