It was announced today that Sony will be performing network maintenance on Monday, January 27th from 12:30 PM to 6:30 PM Eastern Time with the maintenance expected to last approximately 6 hours.
If users have signed in to PlayStation Network any time since January 20th they will still be able to play games online and access partner apps such as Netflix during this maintenance period, however the PlayStation Store, PlayStation Home and Account Management will not be available during this time.
Be sure to sign in to PlayStation Network prior to Monday, January 27th in order to access online game play and partner apps during the planned routine maintenance.
Source: Sony