Just D wrote:
All, and especially those who have Nikon D80 or maybe D200, I have a
question.

I wanted to remove some piece of dust yesterday which started appearing on
the shots at the same place and suddenly found that the mirror is not
looking 100% clean as I would expected.

You've seen the explanation about the mirror. However, dust in your
images are not from the mirror, since it flips up during the shot
anyway. If you see dust on your images it's on the sensor behind the
mirror.

--
Ray Fischer