All the time, except when I'm showering (Citizen Promaster dive watch).
While my mobile is usually on me when I'm on my way to work/out to lunch/shopping/out on the town, I can't imagine being so dependent on it that I would carry it around the house, garden, at the beach etc. I don't notice the watch, unless i need to use it, i can't practically damage it, i can't lose it, and when i need to check the time i don't need to haul out my mobile or ask someone
EDIT: As the Don says, i feel naked without it