Here's the announcement in full from https://support.us.playstation.com/app/answers/detail/a_id/2185
In order to continue to deliver you the best online games experience, we will be performing maintenance to upgrade the software for the PlayStation Store on Thursday, August 29. This maintenance will occur between:
- Start at approximately: Thursday, August 29, 2:20PM PT (3:20PM MT / 4:20PM CT / 5:20PM ET)
- End at approximately: Thursday, August 29, 3:50 PM PT (4:50PM MT / 5:50PM CT / 6:50PM ET)
During this maintenance period, you may receive a message that states “Sony Entertainment Network is undergoing maintenance” when attempting to access the PlayStation Store or PlayStation Home.
We will update you with any changes that may occur in regards to this scheduled maintenance. If you would like to receive a notice when PSN is fully restored, be sure to follow the official PlayStation Twitter account and our support Twitter account,@AskPlayStation.
Still under maintenance here. In fact it's been under maintenance for almost a week, I think. I haven't been able to use the PS Store for a few days now. And I just tried again to make sure.
Edit: Ok, I deleted and reinstalled the Store and now it's working.