We discuss instabilities of fluid films of nanoscale thickness,
with a particular focus on films where the destabilizing mechanism
allows for linear instability, metastability, and absolute stability,
depending on the mean film thickness. Our study is motivated by nematic
liquid crystal films; however similar instability mechanisms, and forms
of the effective disjoining pressure, appear in other contexts, such as
the well- studied problem of polymeric films on two-layered substrates.