From my experience, I'm one of the very few people who write manually in a serifed font; in particular, I write 1, l, I, and | very distinctly and use a slashed zero so as to distinguish it from the letter O. I wish more people would do this since it is still sometimes necessary to communicate on paper, and trying to interpret handwritten notes with ambiguous writing can be quite annoying.

Unquestioning faith in calculators.

The same can be said for computers too - except the problem is often worse as computers are far more complex to the point that almost no one understands them fully, and we are encouraged to accept this.