It is shown that shear-force imaging, as is commonly used for distance regulation in scanning near-field optical microscopy, is not a reliable technique for accurate topographic measurements. This is because different materials experience different shear-force damping. Results of the shear-force damping characteristics are presented for a number of different materials, and some consequences of the different dampings for different materials are demonstrated. It is also shown that there are at least two distinct shear force damping mechanisms. Results of imaging small conducting islands on a glass substrate show that the damping characteristics depend on the islands’ size.