You know, a lot of people mention deserts, frozen areas, and the bottom of the ocean on Earth.
What about the top of the ocean? Why no love for floating cities and/or artifical islands? You don't have to worry about a small pressure leak sawing peope in half, for example; breathable air is greatly simplified; transportation is easier (ship, helicopter, plane, and blimp instead of submersibles); engines allowing limited mobility (doesn't need to be a lot) can allow for moving out of the way of storms, wars, or similar problems...or "migrating" north to south to help maintain a nice temperature. Aquaculture can be more easily done on the surface, with fish farms and such around the edges (netted- or walled-in fish pastures).
Come on, love the eternal cruise ship, people!