Sony Computer Entertainment Europe has announced that the PlayStation Network will be undergoing some extensive maintenance which will disable the service for approximately 12 hours in Europe.
From 4:05pm today, you won't be able to sign-in or use any of the PlayStation Network's services. This will apply to the PlayStation Store on both PS3 and PSP.
However, Sony did reveal that if you sign-in before 4:05pm, the system shouldn't log you out - you'll be able to continue playing online.
The maintenance is due to last until 3am on the 10th of March, and there's been no announcement on what will actually be fixed.