@PlayStationBlog:

I’m happy to confirm that PlayStation Store is open and you can now download content and redeem voucher codes. We will update you with the full lists of new content available to PlayStation Network members and PlayStation Plus subscribers here on the PlayStation.Blog in the next few hours.
You may have noticed that the content promised as part of the Welcome Back offer is not yet live. It is currently in the final stages of testing and will be available to download very soon; we’ll be sure to let you know when.

Sources:
http://blog.eu.playstation.com/2011/06/02/playstation-store-is-available-now/
http://blog.us.playstation.com/2011/06/01/playstation-store-is-available-and-updated-now/?utm_source=twitter&utm_medium=social&utm_campaign=Store_60111