Beta invitations are being sent to random PSN users (I believe they're specifically PS+ members, but I could be wrong). Also, it's possible to participate in the PSASBR Beta by creating a Hong Kong PSN account, buying a PS+ sub with that account and then downloading the beta from the HK PSN store. Furthermore, yesterday people had the chance to win one among two beta keys by fulfilling SuperBot Facebook requests.
Response is generally positive from people who are actually playing the game, so I'd like to try it out for myself. No word on a North American or Europe beta yet, though I'm assuming we'll hear something sooner than later by the amount of people getting in. Might just make that Hong Kong account if I'm feeling crazy.