Normally, we don't waste headlines on standard PlayStation Network maintenance, as it's a fairly common practice.
But this one, as they say, is a little more "significant." And as such, it will result in a longer downtime and it'll affect just about everything related to the PSN, so get ready.
According to an update at the PlayStation Blog , the scheduled maintenance will begin tomorrow around 8 a.m. PST and go through 10 p.m. PST; a blackout period of about 14 hours. And unlike typical maintenance sessions, this one won't let anyone sign in for the duration of the work, and users won't be able to access the Store, Home, the Account Management option, or play games online. Furthermore, "PSN-enabled websites" – including the PlayStation Blog – will also be down during this period.
They ask you to check the official PlayStation Twitter feed to see when everything is back up and running. As for the reasons behind this particular round of maintenance, Sony isn't saying.