Sony have posted on the PlayStation Blog to advise of an extended maintenance period that is scheduled for Friday our time.
The outage will run from 5am until 7pm on Friday, March 2nd (that's this week).
The advisory specifically points out that, unlike in normal maintenance periods, people who are signed in to PSN will be signed out. During the time posted above, you will not be able to access the PlayStation Store, PlayStation Home, Account Management, or be able to play games online. The outage will also affect any PSN-enabled websites, including the PlayStation Blog itself.
There were no details as to what the maintenance period was specifically intended to address.
Twitter users can keep tabs on the maintenance by following @PlayStation.