I guess we're all getting it in the future for XBL but heres the 'beta testing' i guess it would be called, you wont be able to party chat or reverse the UI but the plus's:
i didnt want to do it because of not being able to chat with friends but im guess you will get to try all those things for free until the new Live UI is released?The Preview Program will give you the chance to check out ESPN on Xbox LIVE, Zune music, Netflix search, the new Xbox LIVE dashboard, and new updates to Zune video and Family Settings on your Xbox 360
quick link
from majornelson.com , kotaku