#1 I don't know how one can have a "feeling" about what is required to get into competitive residencies given the wealth of data out there about what people do to get into those specialties.
#2 Even if research is important, of the 13 Derm applicants who had zero research, 9 of them matched. Of those with one research project (36 applicants), 25 matched. I am in a research heavy field. The concept that you MUST do research in order to get into a particular specialty is folly.
#3 Scheduling aways is easy and not exactly time consuming.
If I had to guess...
25% 'know' what they are going into and change their mind anyways
10% 'know' what they are going into and end up going into that specialty
40% have a vague idea of what they are interested in and figure things out before MS3
15% have no idea what they are interested in and figure things out by mid MS3
10% have no idea what they are interested in and figure things out by the end of MS3 or beginning of MS4
Trying to pick a specialty before you actually see what they do day in day out is silly. Few students have extensive exposure prior to MS2/MS3, thus, for the majority of students, 'picking' a specialty before MS2/3 is a waste of time.