Due to a tremendous response from our fans, the Xbox Preview program has reached a near capacity level. With that in mind, we are slowing the number of new people we are accepting to optimize for testing. We are thankful for the amount of interest we’ve received to date and look forward to sharing more details on preview opportunities soon
http://forums.xbox.com/xbox_early_access/update_preview/registration_support/f/4582/t/2028788.aspx
Get in while the getting is good. Request to be added by a Preview memeber