Playstation 3 owners are reporting that they have a difficult connect to Playstation Network today. It appears the new slim model Playstation 3 are unaffected, which seems to suggest a hardware problem. Sony's engineer are working on identifying the problem as we speak and you can follow the Playstation twitter for updates.
As for now if you have an old model Playstation 3 you are best advised not to turn it on.
We'll get back with more information is it surfaces.