Now it seems a new method of resizing an image has been demonstrated by two Israeli professors, Shai Avidan and Ariel Shamir which ensures that the image retains both its functionality as well as its clarity. This method is called re-targeting. The idea is to algorithmically determine which areas of the image are important and then delete other areas retaining those which are important.
Re-targeted vs cropped vs scaled image.
At present none of the graphics suites including Photoshop and Gimp provide tools to re-target an image. Perhaps if this new algorithm (or method) is released under an open license, we could see this functionality being incorporated in Gimp in the future. It is popularly known as 'Seam Carving for Content-Aware Image Resizing'.
For now watch this Youtube video which explains this interesting process in more detail.