It looks like we will finally see what the maintenance was about shortly! It should come back up at 1PM PST according to Metal Gear Online's Website. Read full article for details.
Ok, it's back up now. PLAYSTATION Store is still inaccessible and is undergoing maintenance.
The Account Management and PS Store are still inaccessible. That means that some features are still being serviced. The gaming servers are up though, so start up your Call of Duty 4 and what not. It appears N4G is having maintenance. Oh noes!
Everything is back to normal guys. We hope they did something in the maintenance.