I have a Nikon D70 and it seems like whenever I use manual focus everything will look very sharp through the view finder and on the camera screen, however when I open the pictures up on my computer they are almost always out of focus. I am not sure if this is something wrong with my camera, or if I am doing something wrong. I always shoot in manual with a 1/250 - 1/100 shutter speed and as low as of an aperture (usually 3.5 or 4.5) I can get with what lenses I have. Here is the most recent example of a picture that looked really sharp through the view finder but came out very soft and seemingly out of focus. http://imgur.com/omBQsQE That picture was taken at 300mm, 1/125 shutter speed, and 3.5 on f stop.
That's looks like camera shake to me.
You need to use a faster shutter speed or flash. You can trade ISO for shutter speed.
Another alternative is to use a tripod and a long exposure at low ISO. You would ideally trigger the shutter with a timer to avoid touching the camera and causing vibrations.