it really is variable by institution, and sometimes even by department and the role you play within that department.
in general though, institutions have their own salaries for what they think their docs should earn -- not as much as what you would get in private practice, but not crying poverty either. it is usually based on the assumption that they will do X number of hours of clinical work/week, +/- Y hours teaching [residents, medical students] and Z hours research.
so you get your salary, and you usually start of with a susbtantial portion of your time being patient care--you are generating revenue for the hospital (in exchange for a guaranteed salary). at the same time you're (probably) working on obtaining some grants. once you have some grants you can "buy your time", that is, say I want to be in the lab 3 hours a week, my grant would cover that portion of my clinical time. (hospitals or universities usually ask for some ridiculous amount of money in 'indirect costs' to be covered by the grant -- i think it's partly to offsest lost clinical revenue).
as you increase your grants, you can decrease your time in patient care (if your chair lets you).
if you aren't really doing research but more teaching, then usually in your agreement you establish how much time you'll teach over the year, but in general you end up spending a lot of time in patient care.
thanks for the reply. i understand how the dynamics may differ varying from department to department, but how about subspecialties within a single department? what if doctor X (dollar generated per hour of work) is greater than doctor Y (dollar generated per hour of work) within the same department? i.e., a facial reconstruction ENT specialist versus a head-neck cancer ENT specialist. are they both making the same salary if all other factors are equal (positional status, tenure track, research hours, clinical teaching duties, etc.)?
that's a great question. i'm not sure i know the answer to that. from what i've seen, when you get THAT subspecialized, the doctors don't necessarily become hospital employees -- instead they make some type of agreement with the hospital, i.e. in exchange for providing or renting space (private office within the hospital) i will do my cases here (since surgeries bring in dollars). these private academic physicians (almost a contradiction in terms huh) end up doing their own billing, so they can get a pretty penny. so using your X and Y, X would probably generate more than Y, all things being equal because they wouldn't necessarily be employees. make sense?