Technically, the beta is still playable. You can create levels, but you can't upload them to the server or download missions made by others. Sucker Punch hasn't given a definitive end date for the beta, but whatever date they had planned internally will now be extended by at least five days.
Sony made the decision to take down PSN late Wednesday night, when the system suffered an "external intrusion" -- otherwise known as a hacker or hackers. The company is now rebuilding PSN to make it more secure, but in the meantime it hasn't comment on the possibility that personal information has been compromised.