Some time ago I had the idea of a 'travel bulletin' app using twitter, that would feature a location and info hash and allow you to subscribe to different levels of notification for different parts of your commute or where you live etc.
It was eventually scrapped due to the complexity of the user interface and the lack of ability to adapt to a user's habits. Google Now blows my idea out of the water by providing that up front information from the users habits.
It has the potential to completely seal the mobile market for Google. I know I won't buy another device that doesn't have this feature.