I did just over 3100 cases in my residency where I listed myself as primary (I'm sure not all of these were truly primary, but I bet I fudged that on less than 5%) which boils down to about 64.5/month. We had a heavy peds experience, though, so I did 400 or so tubes and tonsils on my jr 3 month rotation at the children's hospital (133/month). It was not unusual to do 17 cases in a single day running 2 rooms with one attending.
Although I agree with my colleagues above that volume isn't everything, it is definitely a key ingredient. Residency is your chance to make mistakes. I can't tell you how hard it is to see my older colleagues in the community try to learn techniques that I developed as a resident. For example, the 50yo+ guys trying to learn modern sinus techniques doesn't translate well in a significant number. Untrained docs trying to perform minimally invasive thyroid surgery in under 90 minutes or even within 3 hrs for some of them. Guys that did traditional septos for the last 20 yrs trying to figure out how to do it endoscopically. That sort of thing. Moreover, you can't beat experience. You just can't. You can learn medicine by reading a book. You can learn how to treat sinus disease, dizziness, ear infections, reflux, etc by sitting on your couch. But you can't learn how to do surgery that way. There's just no comparison.
Although I agree with Oto-HNS that you know how to do a surgery after 15-20 cases, I would disagree with others who have the idea that once you do 15-20 sinus cases, you've got it. Certainly you can be more comfortable, but I would not want to graduate having done only 15 maxillary antrostomies. I still learn in almost every case I do and I'm up to about 2500 sinus cases now (not codes, but patients). I think the same can be said for ear surgery, H&N, and even laryngology.
I would rank case volume as primary surgeon as the number 1 or 2 in terms of where to go for residency. Overall perceived quality would be the other complimentary criteria. A distant 3rd for me is location. But that's for me--a guy who knew he wanted to be a non-academician. I wanted to be the best ENT in whatever city I settled. I thrived on my surgery skills over my lacking intellectual prowess. I guarantee I wasn't the smartest ENT in my program and am not the smartest in my community, but I bet most would say I have the best hands (at least in the realm of what I do). It doesn't take long for the OR staff and anesthesiologists to get word out about who is great in the OR and who isn't. In the ENT world, we need a balance of brains and skill to thrive. Hopefully my lack of functional IQ is made up by quality OR work which I owe in large part due to my residency surgical volume.