Not everyone is willing to let Google track and store their Web History (that is everything you've ever searched for on Google). But, if you're willing to share that data with the Goog, Google Now will display cards related to recent searches.
For example, if Google detects a pattern in searches about sea otters, a card will appear in Google Now pointing you to more information about them.
Or, if you tend to read a specific blog (like CNET!), a card will appear when that blog publishes new content.
Picking up a friend from the airport? Keep tabs on the flight with a dedicated Google Now card. To enable this, just search for the flight number. The next time you launch Google Now, the card will appear.
Note: Web History must be enabled to use this feature.
In typical Android fashion, you can use a third-party app to add even more commands to Google Now. Here's the full step-by-step on how to use Commandr to make Now do things like read new e-mails, lower the ringtone, and even toggle settings.