Several programs sent me follow-up letters or emails saying that they would rank me highly or hoped to see me next year. A couple told me that they would be touching base with me during late January/early February.
A few programs told me on interview day that they did not have any contact with applicants following interviews.
I wouldn't worry too much about not hearing from programs at this point. Many places are still interviewing and might want to look at all applicants before sending out any letters/phone calls. Also, you can't put much stock in what the PDs say about their level of interest; for all we know, they could tell half the people they interviewed that they will rank them highly.
Edited to add: A few follow-up letters I've received I felt were genuine because they were so in-depth or I received letters from multiple people at the program. I doubted that the people who sent them would have enough time to send similiar letters/emails to each applicant since they were very long and were obviously not form letters as they had so many specific references to my application/interviews.
