Frankie over at the Bungie forums has posted a response to the 30 min delay. To get some of you caught up users trying to download it via Crackdown still have the beta option grayed out. Frankie responded with the following message:
Crackdown Delay: We Know!
Posted by Frankie at 5/16/2007 5:22 AM PDT
With any luck this will be a short delay. People enetering the Beta through other methods - Friends and Family, Rule of Three and so on, are unaffected.