Pothos or Epripremium aureum is a fascinating plant and a reliable house plant. Botanists could not believe the difference between the mature form, a vine over sixty feet tall that climbs up trees, and the juvenile form which is a weak climber that never flowers and might reach six feet.
If these plants are well established it is normal for them to loose older leaves on the stem. You will only find the larger leaves up to six inches across in humid conditions with bright diffuse light.
They are not frost hardy and should not be exposed to temperatures less than about fifteen degrees Celsius. (perhaps as low as five degrees in a sheltered location).
Over watering will cause leaf drop but they are hardy and rugged. If the plant does not look good just cut it back so there are a few stems and it will regrow.
@Geek asks about getting pothos to climb. Many Florida growers are now offering pothos which has been grown up a split log or other surface. You can do this to if you provide the right conditions. Pothos naturally grows roots from the nodal points of each stem. I have grown it in a bathroom where the humidity was enough to encourage this. Roots started and adhered to the trim around the window.
All you need to do is provide high humidity and good air circulation and pothos will do what comes naturally.