Just an fyi for all who are wondering out about schools who may present acceptances without interviews, Princeton had a handful of their prospectives that never received interviews. In fact, the post about the grad student from that school was definitely the more accurate timeline. Three things to take away from this: 1. Despite many good intentions, the results page and postings may not be worth a damn in many cases. 2. Schools are definitely off their previous timelines. 3. Don't give up hope!
In regards to Harvard: Only one person has mentioned interviews. One. For Harvard. I had some contact with some faculty there about a research question on February 10th. While applications were mentioned and people are usually good about breaking bad news if asked, there was no indication that make-or-break interviews had taken place. I would venture to guess that the likely scenario is that if interviews occurred on a wide basis, they were for international/domestic students that may not necessarily afford/be available for a in person visit.
Remember, a request to visit or even funding for a fly out does not guarantee anything. While it definitely means that a majority will receive offers, until you are contacted with funding info and explicitly given the option to join the department, view every interaction as a psuedo-interview.
Oh! And to all those waiting in the wings remember, most visiting weekends will be over by mid-March. Not only will that mean some people may not receive official offers, but that those accepted will hppefully be making a decision ASAP (In which case one may receive that eternally validating feeling of being called off the wait-list that may never have even been mentioned before).
Sorry for the long post, but I wanted to bring info from experience, colleagues work in the process, and professor's knowledge/opinions to this time of rampant speculation!
Hope it calms more nerves than anything!