A variety of novel applications for the investigation of disordered surfaces by beams of thermal energy atoms are discussed and illustrated by numerous examples. A straightforward semiclassical approach is introduced to yield a remarkably detailed insight into the lateral distributions of diffuse scatterers such as adsorbates, vacancies and atomic steps. The recent discovery that the long range Van der Waals force is the cause of the unusually large cross-sections for diffuse He-scattering on individual defects and impurities led the authors to propose a new methods of surface analysis. They introduce a semiclassical method, the overlap approach, to give a simple and detailed description of He-scattering from disordered surfaces. The method yields subtle, otherwise hardly obtainable information on the nature of interactions between diffuse scatterers. The authors address such questions as the lateral distribution of adsorbates, two-dimensional phase transitions, surface diffusions, and the morphology of growing or sputtered layers.