I was on the waitlist for two months before getting accepted. After my interview, I called Bonnie Laster to get some feedback. I let them know that I didn't feel like I came across as myself in the interview (don't do this unless it's true). Also, in my thank you letters, I made it clear that it was my first choice. At this point, a letter (or email) of interest would not hurt. PM me if you want to talk specifics.