PlayStation Network will go offline today for approximately 13 hours, Sony’s announced on the US PS Blog. ”Scheduled maintenance” is the reason given, so no panicking!
The PS Store, PS Home and account management/registration will all be down, along with the Music Unlimited & Video Unlimited services.
As usual, those who are signed into PSN before the maintenance should remain signed in, though said services will still be inaccessible.
The maintenance will last from 8AM PST (4PM GMT) until 9PM PST (5AM GMT, Friday).