Just to add to what Altruist said, they usually take about 100 students on the wait list. They took 60 something from the list for c/o 2011, but it has been going down from there. Each class is supposed to be 160, but ours started out at 168, so they do offer a little more than we can handle knowing that there will be losses. They have to interview to their set date every year, and they are very fair about giving everyone an equal chance (I was accepted from a feb interview and a friend was accepted from the last interview of the year). Usually, if you make the ranked list, it is very likely you will get an offer. In the past, if you are ranked and do not get offered a seat, they have offered a seat for the next year's class so you do not have to go through the whole application process again. I am not sure if they are still doing this with the number if apps that we have been getting though.
This year, one of the admissions ladies - the good one actually, has been out on medical leave for a long time, so if they are not keeping in touch as well is it because she was fantastic at her job and now they're short staffed. I know that this wait is torture, but hang in there! It may seem like there isn't time for everything that you need when you get notified in late May, June or even July on occasion, but the school is flexible with timing for some of the requirements (there is a long list of drug tests, physical, ppd, background check, etc that they need for you to matriculate).
So, good luck to everyone waiting! If you haven't sent in a letter of intention or spring grades, send them! Keep them updated on your activities and make sure that they know that you want to go there.