The Beta release is now available http://www.jthink.net/jaikoz/jsp/beta/start.jsp configured to run against the Musicbrains NGS Test Database. This test database is configured just like the production database and has already undergone alot of testing so it should be very stable. But this has meant a delay in it becoming available and the full release of Musicbrainz is less than two weeks away, so if you want any more changes to Musicbrainz best to get in there quick.
One of the exciting new features of Jaikoz is the ability to be able to add new releases to Musicbrainz. But remember this is only a test database so only add new releases for the purpose of testing, they will be lost when Musicbrainz goes live.