NonneFeminae

I just sent one of these, and I think it can be pretty simple, with varying degrees of detail depending on how much interaction you’ve had with the school. The format that I followed was: 1. Thanking them for their interest in me and offer of admission 2. Letting them know that I appreciated the interactions I had with faculty members (i.e. my interview), and 3. Letting  them know I had decided not to accept the offer. 
 
The response I got was very positive, I think they were thankful I got back to them early because that lets them offer a spot to someone else. Don’t worry too much about it, all departments understand that most applicants apply to multiple schools, so they are prepared to receive these emails. One thing I would advise against is telling them which school’s offer you plan to accept (just not necessary). I hope this helps
And congrats to all the admits! I haven’t heard from Princeton but I wouldn’t be too heartbroken cause I have other options. 

Figure I'll chime in:
I've heard from Boston and was told I'll be contacted presently (hopefully for an interview).
I interviewed with Rutgers last week and Johns Hopkins on February 1st. I was accepted by Hopkins informally from the chair via email two hours after that. That is my first choice because of their strong burgeoning Neo-Latin programme, and I'm elated to work with Shane Butler.
I'm waitlisted at UVA and UCLA. The latter is a tempting prospect.
Still nothing from Cornell or Chicago. Sounds like others have heard from both of those schools, though, so I'm not expecting anything positive from those. All in all, I'm fairly sure I'm going with JHU, but I'll have a better idea when I visit in March.
 
Good luck to all. This process is hellish, but not as hellish as a job outside of academia.

Been lurking for a while so I figured I might post. I’m an undergrad applying in Philology. 
So far I’ve been accepted by UWisconsin Madison and CU Boulder, rejected by Chicago, and interviewed at USC and UIllinois U-C. I haven’t heard anything from the ones who interviewed me, but I know USC sent out offers about a week ago and I haven’t heard anything from them, so I’m assuming I’m waitlisted. Has anyone heard from UT Austin or from UToronto’s MA program? I know someone mentioned they got a funded offer from Toronto a while ago, but I didn’t know if they did PhD and MA funding/decisions together or separately. 
 
Congrats to everyone getting acceptances and good luck to those of us still waiting for news!