You can determine your current city you are in through iPhone's location aware weather app. Just swipe all the way to the left-most screen and see the city name up top. While this certainly falls into the "duh" category for 99% of you people reading this, the usefulness of this makes it noteworthy for the following reasons:
1. You are driving through a densely populated area like Southern California where you could be in a different city from one block to another.
2. You're using someone else' iPhone and don't have your own fancy GPS app to tell you.
3. It's easy to pull up the weather app and also get a nice forecast while you're at it.
4. Some other reason that I can't think of right now, but maybe you can?