Typography issues

A pet peeve of mine is when a zero and the letter "O" are unintentionally interchanged in text (usually noticeable by the width and eccentricity of the glyph). The most common transgression is for people to write "H20," presumably because having a numeral nearby makes people's brains translate the "oh" sound ("O" for "Oxygen") into the number that is often read as "oh." Of course, I've seen in signs and other text where the converse has taken place.

I grant that I'm occasionally guilty of mistakenly hitting the wrong key (since "0" and "O" are adjacent on the keyboard), but I usually notice and correct it immediately...