The PlayStation Network will go offline for scheduled maintenance on Thursday, starting at 8 a.m. PDT and concluding around 11 p.m. PDT (16:00 BST-8 BST Friday). Expect to see the message status that “PlayStation Network is undergoing maintenance” if you attempt to access the PSN or Home.
You can still play online and you can use apps like Netflix and Amazon Instant Video during this downtime so long as you have signed into the network within the past five days prior to the start of maintenance.
Scheduled maintenance will impact both North American and European regions. You may still collect in-game trophies and they will be synched when you the PSN is back up and running. According to the PlayStation Blog, this is simply regular maintenance.