Just about every phone I've owned, I've made efforts to be extra-careful with. I usually get the screen protectors, i don't slide them around hard surfaces to get scratched up, and if I drop a phone, I do freak out about it, but eventually I end up coping.
So far I've been extremely lucky with my iPhones and haven't dropped them without them being well-padded in a case. I also have an Invisible shield to avoid scratches.
Even so, I wouldn't go overboard. Fortuantely the use of cases and skins account for most everyday use, and so I don't have to be overly ginger. But if something happens and I can't help getting my iPhone scratched or cracked, well, I'll have to live with it, is all. Worst case, I've got SquareTrade.