There is an important piece to this story that is missing from all the current news articles: a different earlier post on pastebin, dated 9/2, did
not make mention of any kind of ransom:
http://pastebin.com/zdU1TK40
That earlier post simply said "The group will release all available files to the public on the 28 of September, 2012."
That says to me that a second group saw the original post and decided to try and make some money off it as a scam. Of course it's also possible that they just changed their minds over the weekend.
I'm not sure what either scenario says about the likelihood that this is real, but it definitely makes things more interesting. It's also worth noting that PWC is currently saying they have seen no signs that any data was taken.