Recently I shot some test pictures with my Nikon D80 and a Nikkor 50mm f/1.8 lens. To my surprise, there appeared to be an inconsistency in exposure. I shot exactly the same scene at f/1.8 and at f/2.8. The exposure at f/1.8 seemed perfect, but the shots at f/2.8 were over exposed.
The test photographs can be seen at my Flickr Photostream.
Ken Rockwell discusses the D80's propensity for over exposure. Searching on Google reveals many others have faced similar problems.