When Niantic removed the not entirely functional three step tracking found in Pokémon Go, and disabled third-party tracking apps, there was a bit of an outrage among the community. Now with the latest update (1.30 on iOS, 0.33.0 on Android) a new tracking system has been implemented called Sightings. While not helping you much in terms of actual tracking, it should now update and be more accurate when it comes to showing what Pokémons have spawned in your vicinity (still around 200 metres), and it updates about every 10 seconds to reflect what Pokémons are available nearby. The new tracking feature is being tested out now, so the exact UI may change. Hopefully there will be a reliable way to track nearby Pokémons soon.
The update also fixed a bug related to giving players the proper XP bonus for nice, great and excellent throws. It also allows you to switch your user name.
Thanks, Redditor AlbelTelWicked for detailing some of the changes.