My parents use their email inbox as a filing system. Specifically, a top of bucket filing system. They need something? Email it to them. Did you email it to them? Email again. They can find it if (and only if) it's near the top of their inbox.

A special kind of insanity that puts me in a mild, cold sweat. Such filesystems can come for your family too!

Worth noting, my father was an early adopter of the home computer. It's somehow regressed over the years.