I'd like to point out amidst all the "WHY WOULD YOU HACK A LEGITIMATE CORPORATION" outcries:
There are very well-loved white-hats who do similar (albeit not quite as malicious) things in order to attract necessary attention to security flaws before they get discovered by the real criminals. Look up Dan Kaminsky for the Ur-example of this.
They go about it in more professional ways, generally, giving the businesses affected a reasonable length of time after the exploit before making the vulnerability public, so that a fix can be implemented or at least started. But they still break in.
There was an especially reminiscent incident posted on Slashdot a while back about a guy who sat in an Internet cafe and got access to Facebook accounts of people in the cafe, logged in as them, and sent them messages basically saying "You have been hacked. Stop sending private data over unsecured connections on public wireless."
I seem to remember Kaminsky stealing Youtube traffic and rerouting it to a fake site or some other publicity stunt like that with his DNS hijacking/spoofing attack.
So yes, the Lulz Boat is almost certainly doing it "for the lulz". That doesn't mean that there wasn't another motive. I'd argue that bringing attention to the vulnerability before, say, someone with a botnet for e-mail spam or identity theft found it, is very much worth the lulz. Assuming that this group doesn't act like typical Anonymous idiots by making the personal information public, that is.