PlayStation blog noted the issue yesterday, stating that some folks were "experiencing intermittent service" and saying Sony was "working on finding a solution."
"We are currently investigating, including the possibility of targeted behavior of an outside party, "Sony senior director of corporate communications and social media Patrick Seybold told us this morning. "If this is indeed caused by such act, we want to once again thank our customers who have borne the brunt of the attack through interrupted service. Our engineers are working to restore and maintain the services, and we appreciate our customers' continued support."
A manifesto declaring the group's intentions was posted, which not only declares loyalty to George "Geohot" Hotz and Alexander "Graf_Chokolo" Egorenkov, but also states intentions to "attack your [Sony's] private property because we disagree with your actions." While the group acknowledges this is "wrong," the idea is to mimic what it believes Sony to have done -- restricted the actions of folks trying to use an object they own.
Additionally, Ars Technica reports that the group is encouraging people to show up at Sony stores on April 16 and complain. Nothing quite says "stick it to the man" like complaining to retail employees.