I'm pretty obsessive, every time, from mowers to cars, the dipsticks pulled and checked each time before its started, of course not more then once a day
Every Saturday or Sunday the motors get the quick glance over. I then pull the dipstick to make sure level is full. I add when 150 ml is needed. Only takes 10 minutes for 2 vehicles.
I was the type that hardly ever checked the level do to no consumption, but then had the intake hose split in half for who knows how long.
Every other tankful. Its easy while your right there at the gas station. Also the gas station is the only place where people DON'T ask if something is wrong when the hood is up.
i'm really around the bend. Sometimes on my breaks at work, I'll walk out and check the oil level just for relaxation. This happens about three times a week.