I had an appointment in my phone (synced to Google Calendar) for 1:30pm today. Inside the appointment, I had the address listed because it's somewhere I've never been.

I ended up deciding not to go, but didn't remove the appointment from my calendar. About two hours before the appointment time, Google Now told me I had to leave now to get to my appointment on time with traffic. The card also showed an image of the route with surrounding traffic info.

It would have come in pretty handy.

I seem to recall telling Google Maps my home and work address at some point through the website. I just have to type "Home" when getting directions, and it will input my address into the field. I assume Google Now uses this information.