Sony has announced that PSN will be shut down for essential maintenance tonight between 16:00 and midnight.
Throughout this time the following services will be unavailable – PC registration, account management and account registration. Those signed in before 16:00 will remain logged in and can continue as normal, though logging in will be impossible throughout the period.
The obvious conclusion is that Sony is about to reintroduce the PlayStation Store, which has now been offline since April 20th.