well i would put the blame at 75% hackers, 25% sony.
sony could have handled the situation a lot better.
first of all filing a lawsuit against geohot who is considered a bit of a legend and a favorite amongst hundreds of millions around the world, a bit like filing a lawsuit against princess diana, they should have just offered the guy a job but were too ignorant/stubborn to do so. geohot would have firmed up their security (preventing hacking of the ps3) and they would have gotten a lot of good press for employing an internet legend. a win win situation for them, they chose to try and sue him or put him in prison instead, epic fail.
they removed other OS a feature of their consoles (i never used it but im sure some people must have and i know plenty of research scientists used it). this again further enraged people.
they then targeted firmware hackers/modders getting several sites shut down and lawsuits against them, this was only going to go 1 of two ways, hackers get scared and stop, or hackers get angry and do worse. they chose to do worse and hack psn.
a lot of this could have been avoided, sony really do need a western mind's input into a lot of the decisions they make, someone who knows good PR and can spot marketing opportunities that they blatantly missed.
the hackers did it so most of the blame lies on them, sony basically enraged them into doing so. also their security should have been a lot better in the first place, hacking a network in which 70million plus people rely on is ridiculous. never mind forcing the company to its knees for god knows how long, sony are at the mercy of its engineers and programmers now, it took 10 years to make GT5. this new network could take a lot longer than expected.