Camerashake is one of the major reasons for unsharp images. Not every photographer can hold a camera steady at slower shutter speeds. Therefore try to follow the rule of choosing a shutter speed equivalent to the lens' focal length. Slower speeds may lead to camera movement and consequently unsharp images.
For some time now manufacturers of zoom lenses and telephotos have been offering a feature called image stabilization on their more expensive lenses or high-end binoculars. Canon was the first to introduce the system on their 300mm IS-lenses while Nikon followed suit with their VR-types.
Image stabilization helps to steady the image projected back into the camera by using floating optical elements, which serve to compensate for vibration caused by the user.
The system features gyro sensors which correct jerky hand movements that would normally lead to camera shake. It is claimed that handhold shots are possible at shutter speeds 2 stops slower than with the system turned off.
The system has been available in digital video cameras with large zooms for quite some time now and has proved to be very effective. Only recently manufacturers of digtal still cameras have also started featuring image stabilization. Notably Sony and Olympus have incorporated it in some of their models and other manufacturers may well follow.