UPDATE: Sony has confirmed that the maintenance has been delayed and will not be going ahead. Game on!
Sony have announced that the PSN will be undergoing more maintenance tomorrow on Thursday 1st March from 16:00 until 07:00 on Friday morning.
As per usual, the PlayStation Store (PC and Console), Customer Account Management, and Account Registration will all be out for the count during that time.
It's also worth noting that although in the past users signed in already have sometimes been able to stay logged in, this will not be the case tomorrow. Sony say that "users who are already signed into their account on PlayStation Network before the start of the maintenance will not be able to stay signed in to their online session and will be signed out at the start of the downtime period."
Let's hope the leap year doesn't break everything.