According to the official PlayStation Blog, the PlayStation Network and related services will be down for maintenance for around 13 hours. How will we survive, I wonder? Beginning at approximately 2pm GMT / 6am PDT / 9am EDT various PSN services will go offline as Sony tinkers, tweaks, and upgrades them. The maintenance will last until approximately 3am GMT / 7pm PDT / 10pm EDT.
PlayStation Vita, PSP, and PS3 users won't be able to use any of the PSN's various services obviously, so if you are wondering why something seems messed up today, now you know. And as GI Joe says, "knowing is half the battle."
"We will continue to provide as much information as we can regarding any future maintenance we need to schedule," the blog post notes. "Keep your eyes on the PlayStation Twitter feed for a notice when PSN is fully back online. We look forward to gaming with you all when the maintenance is finished on Monday night."