Hello, there is a press release that was just posted by Sony. All PSN (including PS Store) will be back online worldwide with the exception of Japan, Hong Kong, and South Korea. It will resume all services on June 2, 2011 which is tomorrow.
Update(1): Welcome Back package will not be available until sometime later. Expect some delays and errors when you try to access PS Store as many will be trying to access it at the same time.
To see the press release yourself click : Sony Press Release PSN Restoration"
"Tokyo, June 2, 2011– Sony Corporation and Sony Computer Entertainment (SCE) announced today that Sony Network Entertainment International (SNEI, the company) will fully restore all PlayStation®Network services today June 2, 2011, in the Americas, Europe/PAL territories and Asia, excluding Japan, Hong Kong, and South Korea. The company will also resume Music Unlimited powered by Qriocity™ for PlayStation®3 (PS3®), PSP® (PlayStation®Portable), VAIO and other PCs."
- Sony Press Release