Back in first-edition D&D there actually were XP penalties and other consequences for drifting or changing alignments, but I can't remember whether the third edition even suggests doing such a thing. Sure, there are still alignment-based spells and powers, and Paladin characters still have to maintain a Lawful Good alignment in order to keep their abilities; but there's no necessity for all characters to conform to a predefined alignment of the player's choice, and so far as I recall, no penalty for nonconformity. This makes some sense too, as the game isn't really about differing moral/ethical viewpoints and the clashes between them, and hasn't been in a long time if ever.
However, that doesn't mean the concept of an alignment system is necessarily totally bogus. Are there games today that do make use of defined moral codes and penalize or reward players based on their conformity to the code of their choice? Can a good game be made around an alignment system, and if so, to what end?