If you frequently use public transportation, Cortana has a nice little surprise for you. Cortana can now alert users in the US and UK about public transit, with notifications for calendar events, as well as updates on delays and outages on buses and trains.
I believe it's started rolling out to 930 handsets, but when it reaches others is dependent on carriers. Could be next week, could be next month, could even be a little longer. If you want it earlier (right now), consider enrolling on the Preview for Developers.