35+ years ago in college it troubled me that among the first lessons learned in basic statistics was the necessity for employing "random samples" in research studies, even while in reality samples I saw in academic literature were virtually never truly random (indeed, the very concept of a really "random sample" is questionable).
35 years later, nothing has changed, but a journal paper by some behavioral psychologists, now making the rounds, entitled "The Weirdest People in the World," is highlighting this concern over how representative research conclusions from limited samples can be for humans in general.
fuller citation here:
Henrich, J., Heine, S. & Norenzayan, A. (2010) "The Weirdest People in the World?" Behavioral and Brain Sciences. [PDF] [Audio File Part I] [Audio File Part II] [Coverage in Science]
Neuroanthropology blog has addressed the paper in an extensive blog post:
"WEIRD" people, BTW, are those from "Western, Educated, Industrialized, Rich and Democratic societies."
I'm just glad to see the issue getting the attention it deserves (and I'd add that while the criticisms raised are being principally pointed at behavioral and psychology studies, even biological/physiological research in humans is not entirely immune from such questions/concerns).