From a few other posts and personal experience, it seems like if you don't get something in the original wave (or two) from a program, odds are that you won't be offered an interview there. It seems like some of the programs do send out a second wave a week after the first (Duke did this, Carolinas Med Center, Penn State, I think, and Hopkins might be planning to...), but after that if you haven't heard anything, I wouldn't get your hopes up. Stanford, for instance, have allegedly sent out the only interview offers they plan to send, but have not sent out rejections.
Also, keep in mind that it's still early, so wait lists won't be moving as much because people's schedules aren't filled yet. I'm hopeful that in the coming weeks, wait lists will start moving a little bit as people turn down or cancel offers that conflict.
Just my two cents, and good luck to everyone. This is a frustrating process...