If you're reading an article about George Washington, for instance, it instantly knows who you're talking about when you ask: "Ok Google, when did he become president?" No need to specify who "he" is -- the assitant even dictates the main answer in addition to returning the typical search results.
If you're reading about a certain location, say Disneyland, you can ask "Ok Google, how do I go to this place?" and it will tell you how to get there by car or other means. The latest version of Google for iOS also returns more detailed local search results and lets you copy-paste from anywhere in the app. You can download it right now from iTunes if you want to be able to do more hands-free search queries.