The PlayStation Network will be going offline on Monday afternoon for most of the night while maintenance work is carried out. In total, the PlayStation Network will be down for 9 hours, between 4pm and 1am the next morning. There hasn’t been any downtime recently, surprisingly.
The maintenance window will begin on December 3rd 2012 at 4pm, but signing in before will let you continue playing online without disruption. As usual, other PSN services will still be inaccessible during the maintenance, including the PlayStation Store and Account Management features.