I was on the UVM waitlist last year, called on May 1st, and was told that I was at "the top of the top 1/3" and that my chances were good. I don't remember who I talked to. Anyway, in the beginning of July I received an acceptance letter dated June 10th, with the usual instructions of responding in a week with a deposit, etc. According to the date on the letter, it was too late for me to respond anyway. I sent them a letter withdrawing that same day, explaining in it the belated delivery of the letter so that they didn't think I just sat on the acceptance and so that they knew it had arrived late. One day later, I received a letter from them that since I "have not replied" to their offer, they were withdrawing my application and notifying "the board" (who's "the board", well, I don't remember exactly what it said, but it was sort of a "We are withdrawing your application and you are grounded for a week" reprimand letter. I called and explained the situation, they understood, and it was all good. The point - stay on top of calling! I was already in at my first choice, so losing the acceptance against my will wasn't a big deal to me, but I wouldn't want it to happen to anyone else.
For those wondering why I left my name on the list at UVM when I knew I wasn't going to go there: I passed out during the interview. It's a long story, but I interviewed in September, was ill, etc. and at the end of my interview I stood up to shake their hands and passed out cold. I somehow sprained my ankle on the way down and left the interview on crutches. After I was accepted where I wanted to go, my application became an experiment, "Can one FALL DOWN at the interview and still get accepted?" Wouldn't you have wanted to know??
Anyway, good luck w/UVM, and keep on top of them, call every two weeks or something.