We've blogged about a bubble wrap "stained glass window" before, but bubble wrap also works as a great insulator when it's cold. See how to use leftover packaging to decrease your heating bill, after the jump...
According to Build it Solar, bubble wrap is often used to insulate greenhouses during the winter — so why not use it at home, too! As an alternative to insulating shades, bubble wrap provides a pocket of air to prevent cold and heat from moving in and out of your home.
While it obviously doesn't provide the regular view you're used to, it does skew the view inside, thus preserving your privacy.
Recommendations from Build it Solar include using larger bubbles and using a film of water (applied via spray bottle) to get the bubble wrap to stick. Evidently, it will stay in place after application - no tape or anything.
Alternatives to bubble wrap insulation for your windows that might look better can be found via ThisOldHouse.