A new update for Google Maps was released today and brings some impressive new functionality. Artem put it well (although perhaps not exactly eloquently): "it's #$%^ing amazing... Google keeps blowing minds." In a nutshell, Transit Navigation (as it's officially dubbed) brings exactly what you'd expect - it helps you navigate public transport. In their words:

Transit Navigation (Beta)
Google Maps Navigation (Beta) currently provides over 12 billion miles of GPS-guided driving and walking directions per year.