I hope you didn’t have big PlayStation Network plans today — the service will be undergoing maintenance today. For 11 hours.
What this means is that you “may” not be able to access the Store (hope you PS Plus users got your Mortal Kombat demo already!), you “may” not be able to sign into PSN, and you “may” not be able to play online games. You know what, forget the “may” — just plan on not being able to do any of that stuff, okay?
The maintenance is scheduled to start at 8:00 AM Pacific Time, or 11:00 AM for you folks on the East Coast of the United States. Eleven hours is tough, but I think you’ll live. Try, I don’t know, doing something else.
PlayStation Network Maintenance on March 9, 2011 [PlayStation Knowledge Center]