The disclosed computer-implemented method for classifying electronic files may include (i) identifying an electronic file that is being evaluated for importance by a file-categorization system, (ii) collecting, via at least one user-state monitoring device, information about a physical state of at least one user while the user is interacting with the electronic file, (iii) determining, based on the information about the physical state of the user while the user was interacting with the electronic file, whether the user considers the electronic file to be important, and (iv) classifying, by the file-categorization system and based at least in part on determining whether the user considers the electronic file to be important, the electronic file as an important file. Various other methods, systems, and computer-readable media are also disclosed.