Thank you all for your inputs. Deck experience apparently varies considerably mainly depending on the weather. We enjoy relatively good weather in Northern Virginia with long and gorgeous springs and autumns, summers that can get hot and humid, and winters generally mild but sometimes surprising with lots of snow.
But regardless of weather, sounds as if best anyone can hope for with deck maintenance products is five years on horizontal walking surfaces. That still surprises me. I would have thought that somewhere there must be some miracle coating that lasts 10 years or so.
However, another major factor in deck wear could be that all four surfaces (top, bottom, sides) on horizontal boards are rarely if ever coated. Usually only the tops are painted with a little seepage into some sides.
Presumably evaporation from the ground pentrates the untreated board bottoms and aggravates the problem? My second story deck bottom is high enough that I could paint it, but I'm too lazy. My deck is about 440 square feet plus steps, so it is not a casual job even for painting just the top surface.
It's interesting the different experiences we have with products. I always start my research with Consumer Reports but I don't always agree with their conclusions (e.g., their latest digital camera ratings don't even mention the Canon PowerShot Digital Elph SD200, which is my favorite all-around camera).
And sometimes they have to eat their ratings after initial tests. Some of their car and other equipment choices have plummeted after reliability problems. Since reliability (endurance) is a separate issue from ideal new performance, some changes over the years are understandable.
I like the CR idea of continuing evaluations of paints based on how they fare each year after exposure to the elements in their tests. Some paints have such poor endurance (at least in the CR tests) that CR no longer rates them.
I probably have underestimated the effects of weather and general environmental influences on my house and deck. My own litmus test is a glass table on a covered porch. Within two or three days, in our apparently clean general suburban environment, the glass table top is covered with grime.
Much of it is pollen, but much also is plain ol' dirt. So I guess after all this research and introspection, maybe it's no surprise after all that decks and other outside surfaces need more care that might be expected.
Unfortunately my deck, well built as it is, is fastened with screw nails. So replacing my horizontal boards with even the lightest maintenance-free composites probably would tear up the supporting beams too much.
So I guess I'll stick with pressure washing and repainting every two or three years. Not what I expected when the deck was built. This year I'll look at a favorite of both CR and Drediock: Cabot, specifically Solid Color 1880 latex opaque. It's expensive at $29 a gallon, but might give me a third year of wear. Hope springs eternal.
