I've gone to Asia for two weeks with a carry on. Middle East for 12 days? Carry on. Same for South Africa, South America, and all over Europe. I'm a hell of a packer (lots of experience packing and repacking on those business trips where I am in a different country every other day), and I like to travel light. Unfortunately, traveling light for business is easy, not so easy for fun trips. The difference? Hobbies.
Sure, high heels take up a lot of suitcase room. But diving fins (Honduras), ice skates (Homestead) and now hiking boots are in a different category altogether. For my recent hiking week in Ireland, I packed boots, waterproof waist pack, two water bottles, emergency first aid kit, emergency blanket, rain jacket, flashlight, hiking pants, water filtration system, Nikon camera, and a shitload of power bars. Result: checked bag.