The PlayStation Network is going down for maintenance today, in the first steps of the planned PlayStation Store restoration. The PlayStation Blog is vague on how long the maintenance will last, only saying it will render the network "inaccessible for several hours."
"The sever maintenance performed at this time represents a crucial step in the full restoration for PSN, including the PlayStation Store," said Sony Network VP Eric Lempel. Sony confirmed yesterday that Store restoration is planned for this week, so this maintenance should be paving the way for it.
We had heard of scheduled maintenance in Europe for yesterday, but it was pushed back. Once the Store returns, Sony is planning multiple updates per week to catch up on content missed during the downtime.