Has anyone experiences a defect in auto-focus with the Nikon 18-135 lens or Nikon D80 body?

Answer 1

I have been using a Nikon D80 since 12/25/2006 with the 18-135 lens. I have not had problems with the autofocus that I would call a defect - but I have had instances where the autofocus doesn't work. When that happens I switch over to manual focus.

Autofocus is essential a computer program. Sometimes there is not enough information, usually a change in colors or contrast, to allow the autofocus program to work. The manual shows 6 different examples when Auto Focus might not work on page 29 of "The Guide to Digital Photography with the D80 digital camera".

The six examples are:

Subject color identical to background color
Subject dominated by a geometric patern
Subject is smaller than a focus area square in the viewfinder
Focus area contains objects that are at different distances
Focus area contains very extreme brightness/darkness change
Subject contains many fine features

Most of the time these extremes don't affect the focus - when they do I switch to manual focus. You can also try choosing a different object in the scene to focus on that is the same distance away from you.

Answer 2

David has the correct answer. I just wanted to add, what I am seeing people complain about is the exposure. Evidently some folks are setting the D80 at a minus 2/3 exp comp routinely.
I just got mine on Saturday, and haven't had much opportunity to play with it, but so far no AF problems.