Microscopists are constantly pushing the limits of what microscopes can show and teach us about cell biology. One group recently used TIRF-based polarization techniques to image events at the plasma membrane during exocytosis. Exocytosis is the fusion of secretory vesicles with the plasma membrane to release their contents outside of the cell. The signal in the image above indicates the submicrometer changes in the curvature of the membrane shortly after the vesicle fuses with it (second image in panel is after fusion; cartoon is interpretation of the images).
Reference: Arun Anantharam, Bibiana Onoa, Robert H. Edwards, Ronald W. Holz, and Daniel Axelrod, 2010. Originally published in Journal of Cell Biology. doi:10.1083/jcb.200908010. Paper can be found here.