PlayStation Network has been down today and is scheduled to return at 12:30PM PST. Sony has given us no details on what the reason might be, other than simply saying that it is due to scheduled maintenance:
“On Monday 8/30, PSN users may be unable to access the Store or certain PSN features from 12am to 12:30pm Pacific time "
This is not the first time Sony have taken some of the features off PSN temporarily for maintenance. But during these scheduled maintenance periods there is no access to the PlayStation Store, PlayStation Home or your Account Management. You are though still able to sign in and play games online.
You can keep an eye on any new updated information yourself by following Sony’s Playstation Twitter feed.