There's a good article in the New York Times discussing the merits of incorporating a spiral staircase in a duplex. For some spaces it's the only option because of structural or design elements in the building. Depending on the size of the space spiral staircases can really free up certain areas if it's possible to move them, and in smaller spaces can take up too much precious space. One key element with a spiral staircase is to view it as an essential design element, that should match well with your sense of how the interior will be designed, and also incorporated as an aesthetic that you won't get tired of looking at. There are a whole range of options, from handmade carved railings to sleek modern staircases without railings like in the image pictured below. While not for everybody, the spiral staircases without railings certainly reduces the amount of visual imprint the staircase as a whole makes.