Photography 41: Weather Sealed Cameras and Lenses, Necessary or Marketing??

Weather sealing is a big plus for any camera and lens combination which will be used outside, but is it a necessity or is it just a nice marketing element? I own Pentax cameras which are weather sealed, but I currently have only one weather sealed lens. The best weather seal is probably just common sense, be careful to keep your camera protected from water and sudden temperature changes. Enjoy.