One of the definitions of great architecture is if it "...is still great as a ruin." Perhaps what our modern cities are missing are great ruins? We routinely design buildings with an intended life expectancy of 50 years. Most minor buildings don't make it even that long, and the materials used in many modern buildings are only viable for about that long. We live in a world that has become acquisitive of the disposable. Those artifacts that outlive their first use are becoming rare, and collectible, while the objects around which our lives seem to revolve, such as cell phones, cars, etc., are tossed away in a moment. It will be very interesting to see in the coming years if we re-evaluate our valuation of things, or if the cycle of acquisition and disposal continues to accelerate.