In an article for About.com's Medieval History section, Melissa Snell discusses feudalism in medieval society, and why it may not have been the "dominant form of political organization in medieval Europe."
Snell offers a definition of feudalism and writes:
Feudalism was not the "dominant" form of political organization in medieval Europe. There was no "hierarchical system" of lords and vassals engaged in a structured agreement to provide military defense. There was no "subinfeudation" leading up to the king. The arrangement whereby serfs worked land for a lord in return for protection, known as manorialism or seignorialism, was not part of a "feudal system." Monarchies of the early Middle Ages may have had their challenges and their weaknesses, but kings did not use feudalism to exert control over their subjects, and the feudal relationship was not the "glue that held medieval society together."
A lengthy discussion of the system follows.