... when one does not know the people or are viewing a group from afar. There might be something to it in some cases, but often there's nothing sinister about it.
I have this problem all the time at the beginning of the semester and it has NOTHING to do with race/ethnicity. AAMOF, this semester I happen to have 5 women who are strawberry blonde, blue eyed, of similar stature with similar hairstyles. It is only because I interact more closely with them in the lab that I have developed an individual recognition of each, but it has taken a couple of weeks. FWIW, the blacks in my class this semester were much easier to tell apart and put a face to the name. As too were the men since I have only two
This issue is just another one that a real observation has turned into a monster of political correctness. Certain races or ethnicities have less diversity in characteristics compared to "white people" only because so many are called white by default. It's just as hard to tell a bunch of Irish or Swedish apart as it is a bunch of Chinese or blacks.
HOWEVER, if a white person made the comment to Noriega that "you all look alike to me", or worse yet had that white been a Republican member of Congress, the press would not relent until that person had resigned from office or been pummelled into obscurity. But since this was a black Democrat, there is no hue and cry. To make it worse, she made these comments in the context of attacking the Bush Administration for being racists! It is a disgusting display of a double standard. 
Evie 