It was found, over two decades ago, that some fluids exhibit a remarkable spectrum of new properties when confined between two atomically smooth and nearly parallel mica sheets in the surface forces apparatus. Oscillatory or structural forces, as well as a dynamic solidification of such thin fluid films were reported. What do these fluids have in common and what can we learn from their behavior? Well-established thermodynamic measurements of fluids adsorbed into porous materials suggest a shift of critical points, transition temperatures and enthalpies, which are more pronounced the smaller the pore radius. Recently, unexpected density and film-thickness fluctuations were discovered in these confined fluid films. Can a shift of thermodynamic quantities in small volumes account for the observed fluctuations? Recent results reveal a relationship between the thickness of the mica sheets and the amplitude of the fluctuations in the eSFA. I will present new details of the contact mechanics at sub-Angstrom resolution and discuss the role of nano-particles in SFA measurements. A comparison of measurements obtained with conventionally prepared and particle-free surfaces is shown. A mechanical model involving nano-particles is invoked to explain the observed effects.