While I'm sure there will be more rational and erudite discussion about the windows, I'd like to offer a few ideas about window weatherization- and I do feel strongly that there is no reason to replace good, old well made windows. All of the basic stuff aside - weather stripping, etc, which goes a very long way toward making them more efficient, I have a somewhat different take on storms than my esteemed colleague Rudy, but agree that storm sash is a great asset. I prefer them on the outside of the window sash for a couple of reasons: I've found that, in the case of my own hut (built in 1796 with 12 over 12 sash, "new" 6 over 6 windows installed in 1805 - an extravagant upgrade), in a part of NY that gets avg 140" of snow a year, exterior mounted storm sash protect the multi-light sash, glazing compound and sills from weather in the winter, so that a repaint every three years is not a critical issue. I also like the idea that the weather is getting stopped between membranes on the outside of my window system, rather than between the inner face of my multi-light sash and another membrane. From a cosmetic point of view, I enjoy looking at the delicate, hand planed muntins on my sash in the winter, rather than the large lights that interior mounted sash would present. Another reason, and this may be totally bizarre from a rational point of view, is that I enjoy very much the process of the "closing up" of the house for the winter, like putting on its jacket for the coming snows and wind - seeing a house with the storm sash on is like seeing your kid bundled up with their hat and gloves. "Opening up" in the spring gives one an opportunity to make the close inspection of the windows, which because of their nature (they really are pieces of case furniture attached to holes in the walls) are more prone to ravages of weather. All of this putting on and taking off require labor, of course, but force you to LOOK at the building at least twice a year and think about what it needs.