What are you doing between 4pm GMT today and 6am GMT tomorrow? If you thought the answer was "accessing a range of PlayStation Network services", then think again, because Sony has said that PSN will be down for maintenance throughout that period.
What does that meeeean though? It means that you won't be able to access the PlayStation Store, PSN account management or registration, PlayStation Home, or the Music and Video Unlimited services. Nor will you be able to sign in through the PlayStation.com website.
According to Sony's US blog, users who are signed in before the start of the maintenance won't get booted off, but won't be able to use any of the above services. Don't worry though - you can still collect Trophies in your games, and your profile will be updated when PSN comes back online.
So that's PSN offline from 16:00 GMT / 17:00 CET / 08:00 PST today, 19th January, until 06:00 GMT / 07:00 CET / 21:00 PST tomorrow, 20th January.