From what I understand, (one of) the motive of LulzSec is to "take down" Sony. Given these recent attacks to follow through on it, I think I have an opinion of what's going on here.
War.
LulzSec is waging digital war on Sony, launching attack after attack in an attempt to get Sony out of the picture. These aren't just some kids poking at files for fun, they are trying to force Sony out of the market by ruining their reputation with these cyber attacks, and if that doesn't work I wouldn't find more meaningful attacks against Sony surprising. Imagine if, instead of swiping info from the PSN, they deleted info from PSN, or took other steps to meaningfully damage Sony's data, we could be looking at the early steps of what a true digital war looks like, even if it's not between countries as we understand them in the physical world.
Just my 2 cents, probably crazy, for all that's known these could just be kiddies poking fun at a corporation, but who knows for sure...