The PlayStation Network is currently down – dead, kaput, not responding. There’s no planned maintenance and this looks like it’s a bit of a surprise to Sony.
“PSN and Stores are currently unavailable,” says a Tweet from the official account. “We’ll let you know as soon as they’re back online.”
The Japanese PSN Status page might hold a little more information, although our translation efforts yield little other than an apology.
There’s meant to be a big content drop today for Modern Warfare.
Update: Sony have now said the PSN is “under maintenance“.
fs
I was playing online at the time you posted this, maybe it doesn’t affect everybody.