All of our floors are hardwood or tile. I love the wood, hate the tile. (I've got kids with allergies, so it's preferable to carpet.) The wood is easy to care for; I just sweep or dust mop.
Our living room is over the garage, but it's extremely well insulated; the floor doesn't feel cold to me. (The kitchen tile does, though.) I have an area rug in the living room for color and to protect the finish from the furniture. (Oy, the scraping!
My kids can't leave the furniture alone!) Our last place was an old house and when we took up the ugly carpets that were there, I did notice drafts - mainly around the radiators and from under the molding. Apparently there were gaps that weren't initially visible. If we had stayed longer, I'd have wanted to re-insulate because it was an expensive place to heat. Our current place is new construction, though and extremely snug.