This happened to me. Several rounds of interviews with a well known colored-hat company, then... nothing. No response to follow-ups either.

What was especially frustrating to me was that up to that point, the tone of both the conversations and email exchanges was very positive and cordial. I would have expected a "Thanks, but no thanks" follow-up at least, especially considering I was an internal referral from a Sr. Mgr. But... nothing. Made my reconsider my view of that particular company.