This. If I'm just going to be out in the sun for short periods of time I don't bother, but any long exposure (and I'm a road cyclist, so I can be out in the sun 4-6 hours at a time routinely) I definitely try to remember to put it on. Otherwise, I'll get COOKED. Sometimes I forget - this January, I was in Chile for a week, and on the walk from our hotel in Valparaiso to the beach I figured I could just wait till I was on the beach. I dind't account on it being an hour and a half walk in direct, equatorial sun, and I was pretty red by the time we got there. I spent the rest of the week alternating between sunscreen and moisturizing lotion to (futilely, as it turned out) try to prevent peeling.