Sony has announced via the PlayStation Blog that PSN will be going down for six hours on Monday January 27 for maintenance.
In Europe the maintenance will take place between 5.20pm and 11.30pm GMT, whilst North America will have PSN down between 9.30am PT/12pm ET and 3.30pm PT/6.30pm ET.
If you have signed into the PlayStation Network any time since January 20 you will still be able to play games online and access apps such as Netflix. The PS Store, PlayStation Home and Account Management will not be available though.