A year ago, my schools aed officers had dinner with the three admission deans of my state´s 3 med schools. i sat next to one of the deans. he mentioned that he ¨hates¨reading letters from instructors. He said that he takes letters from FULL professors most seriously....and he hinted that letters from alumni or disting professors are even better. i think he also said something to the effect of "we dont like to get letter from instructors, at the very least, make sure they are asst professors."
Now, as you see, other admission people will not care (
LizzyM). Just be aware that others may. I got my science letters from two distin professors (one is dept head) and my non science from an asst poli sci prof. i also got a 4th letter from my boss, who is an RN. i was going for the whole "balenced" thing....
Whether it is fair or not, it will be for some admission people important. They value the academic hierarchy(spl?) establishment....take from this what you´d like....