We present two applications of single mol. spectroscopy that illustrate how ensemble averaging masks important dynamic properties of fluctuating systems. In the first, mobile elliptical structural deformations are obsd. in single assemblies of the light harvesting complex, LH2. These mobile structural deformations are averaged in bulk measurements resulting in the erroneous conclusion that LHS is a circular absorber. In the second application, trajectories of individual members of a folding ensemble of coiled coil GCN4-P1 peptides allow us to det. distributions of properties not available from bulk studies.