The PlayStation Network will be shut down for 13 hours today, according to Sony. They plan on shutting down the service from 8am until 9pm PST (which, if my maths is correct, means 4pm until 5am in the UK).
During the maintenance period users will not be able to sign into the PlayStation Store on PS3, PSP, and Media Go, PlayStation Network Account Management, PlayStation Network Account Registration, PlayStation Home and Music/Video Unlimited services.
Sony released this information: "Users who are already signed into their account on PlayStation Network before the start of the maintenance should be able to stay signed in to their online session, but will not be able to access any of the services listed above. Users who attempt to sign-in to their PlayStation Network account after the start of the maintenance may be presented with the site maintenance notification page if they haven't signed in recently."
Don't worry, trophies collected during the PS Network downtime will still be added to your profile once the site comes back online, though anyone interested in getting on with some online gaming tonight, better get logged in early.