And yet some of the worst performance issues I've had to deal with were in code typically dealing will merely 100s of items, but using algorithms and slow netwo

And yet some of the worst performance issues I've had to deal with were in code typically dealing will merely 100s of items, but using algorithms and slow network-based operations that caused everything to run sluggishly most of the time and not infrequently making the resulting user experience intolerable. I do agree though that a lot of time is wasted on premature or even completely counterproductive optimisations for situations where the data being processed is too small to cause noticeable slowness in processing.