As a intern at the U, I can give you some idea of what to expect here.
Are the residents happy here? I would say the answer is yes, the happiest residents being those who love the outdoors and are able to find stress relief from skiing, hiking, camping, or mountain biking. The program here is rigorous for sure, we have more ICU time than some other programs I looked at, and that aspect should not be overlooked if you are looking for the most cush program. However I will tell you that I have encountered only one hostile or malignant personality in an attending so far, which I think is because the program and city attract a certain type of personality, this is a dramatic change from my med school alma matter which will remain nameless. So what makes the program kind of intense is not the people but the schedule. Intense months are very rigorous, that said I know of only one or two rotation where there are consistent issues with duty hour violations and they have enacted changes a few months ago to rectify that (hopefully they continue these modifications), and the easier outpatient months give you plenty of free time. Enough free time that I know of several interns who have already ski'd 15+ days (one is up to nearly 30). We have a snowbird facebook page for interns to meetup on the slopes and share beers afterwards.
I think your feelings about SLC will depend on what you want from the city. If your major stress relief/hobbies in med school were going to bars and clubs and you are looking for a thriving night scene you may be disappointed. There are certainly bars and SLC is likely less conservative than outsider's believe, however bars close on the early side, and generally people here just do that less often. I know a couple interns or their significant others have been let down on that aspect. However, if you are looking to be able to utilize the mountains you will not find a better place to do your residency. You need to be honest with yourself about what makes you most happy.
In terms of ranking the program on a scale of 1-10, i think thats pretty difficult to do. I know we have had a history of killing ABIM boards, and trying to gage the match list success on a program can be difficult from the outside, the most interesting and telling detail is how may people applied and didnt match. I believe many of our residents choose hospitalist gigs out of residency including our chiefs, which I think again reflects the personality of the people here- work hard/play hard kind of mentality. From last year everyone matched into cards and 1/2 in GI, although that person admittedly applied very late in the game for GI. In general many of the people who matched here for residency ranked it at the top of their list above some first and second tier programs with possibly stronger "SDN rankings" if you will. At least I know that I did and I dont doubt my decision for a heart beat.
If you have other specific questions let me know.