Oh, I'd never disqualify an interviewee purely for not knowing this stuff, but it is useful to know.

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Also, I care far less about whether they can solve some problem on paper about asymptotic complexity than if they have some sense of what it means. Someone with little formal training who discovered the classic python "Add to the end of string" algorithm is N^2 and figured out a working knowledge of N^2 vs. N is better than someone who memorized a bunch of math but can't apply it because it went in the "math box"[1]

1: http://zenoferox.blogspot.com/2009/10/deep-inside-math-box.h...

This is categorically untrue if you are talking about large numbers and asymptotic complexity. It is true that algorithms with a constant factor larger number of operations may have such properties, but O(n) will always beat O(n^2) eventually, and in nearly all real-world cases at a fairly small n (1000 L1 cache accesses is slower than 1 memory access so n=1000 will be enough to counter any locality issues).