Transit directions have been a big reason why some people prefer Google Maps to (say) Apple's maps. In places like New York or Tokyo, it's a huge win for users. It's also spawned an open specification (Google Transit Feed Specification) that has sparked a ton of innovation in the public transit space, including real-time location updates from public transit authorities.
Full disclosure: one of the big leaders of the Google Transit project was Avichal Garg, who was a PM for the webspam team when he ramped up Google Transit in his 20% time.
Full disclosure: one of the big leaders of the Google Transit project was Avichal Garg, who was a PM for the webspam team when he ramped up Google Transit in his 20% time.