The Windows Live Folders beta, that was opened yesterday, to the first 5,000 users to get there. With a slight changing of your locale to en-us, many users were able to get in, with or without an invite. While we're not sure that's going to sit too well with the beta testers who didn't get in, at least they're in the Photo Gallery beta.
You can get on a mailing list for the next wave of Folders testing, and truthfully the interface and functionality of Folders is pretty well set, it's scaling it up that needs testing.
Source:→ livesideMicrosoft, Windows Live, Windows Live Folders, Betas, Live Photo Gallery