The larger the magnification of a lens, the smaller the field of view and the greater the variation in image position due to camera movement.
With a telephoto lens it is important to look for additional support at all times so you can hold the image steady in the viewfinder. If you are having difficulty in keeping the image steady in the viewfinder it is more than likely the resulting image will not be sharp or even containing theimage your after.
The general guide is to aim for a shutter speed which is atleast shorter than the resiprical of the lens in use, ie. for a 200mm lens we should be looking for a shutter speed faster then 1/200 ie 1/250th second. Image Stabalising and Vibration Reduction technologies allow us to get away with slower speeds than these guidelines and handhold the lenses more often. But even when using these lenses we should be looking to minimise shake be using the best method of support available and using the shutter speed guideline for the particular lens.
One other area that can introduce camera shake and affect the sharpness of the image is mirror bounce. This occurs in SLR cameras, both digital and film, and is shake in the camera due to the movement of the mirror required to close off the viewfinder to expose the film or cameras digital sensor array. Most compitent camera's have ways of reducing this effect, with the F5 you can lock the mirror up and the D1 allows you to delay the time between mirror movement and picture exposure such that any shake has decayed. However these facilities affect auto-focus and exposure operation not to mention hindering you the photogrpher from knowing what you are photographing at the point of exposure. Often a responcive camera is key to getting that shot and a delay to allow a mirror to settle is counter productive. Another way to reduce the shake in the camera is to ensure that the camera and mount deaden any vibrations a good stong head and tripod are esential for this, carbon fibre is also better than aluminium for this aswell. Also resting your hand ontop of the lens centrally over the point where the tripod mount connects to the lens.