The way I write the numeral '1', I'm in more danger of confusing it with lowercase 'l' than numeral '7'. I believe this is one of those little things that helps mark people out as European or American. (To prevent my numeral '1' from colliding with my lowercase 'l', I'll add tiny serifs to the numeral top and bottom.)

Confusing capital 'Z' with numeral '2' is possible for me; luckily, capital 'Z' is really uncommon in what I create. If I feel it might be a problem, I'm likely to increase the curviness of the top of my numeral '2'.

Anyway, this is all handwriting. Typefaces, which aren't scrawled in haste, have a lot of other tricks they can use to distinguish glyphs.