I've had a ton of people ask me about being on hold recently. I'm sorry to hear about those of you who were put on hold, but hold is unfortunately the most common outcome for people post-interview. My understanding is that there are three possibilities post-interview: you can be immediately accepted, immediately rejected, or put on hold. Most interviewees are put on hold. Hold means that no decision has been made about your app yet. It is NOT a waitlist. Basically, if you are on hold, the admissions committee wants to finish interviewing everyone first before making their decision. They will decide in the spring (April) to accept, waitlist, or reject you. So, for now you should expect to have to wait until the rest of the interviews are all finished to hear any more about your app.
Ok, so the other question I have been asked a lot is what to do to improve your chances of getting off hold and being accepted. I've asked around about that. Basically, you should update the admissions office with any new information you have (fall semester grades, new volunteer activities, awards, etc.). According to Dean Franco, letters of intent (where you promise to attend the school and withdraw all of your other apps if they accept you) are not really necessary, so you don't need to write one. Beyond updating your file with new info, I'm not really sure what else you can do to improve your chances of acceptance. I hope this info helps, and good luck to all of you.