Announced by PlayStation's official US blog, the PlayStation Store is now available and updated now. The content in the Welcome Back package isn't live yet, however, and is "in the final stages of testing and will be available to download soon". Both the PlayStation Store and PlayStation Plus will be updated June 3 and then they "will roll right into special publishes starting next week for E3".
Here are some of the newly available content for PlayStation Plus subscribers (full list):
PlayStation Plus Full Game Trial - Tom Clancy's Rainbow Six Vegas 2, Dante's Inferno
PlayStation Plus Featured Games & DLC - SOCOM 4: U.S. Navy SEALs, Oddworld: Abe's Exoddus (PS one, Free), Sonic the Hedgehog 2 (Free)
Slam Bolt Scrappers - $9.99, dropped from $14.99
Sam & Max - The Devil's Playhouse - Full Season - $19.99, dropped from $29.99