Zeitgeist is a framework that tracks and logs the users’s activities and events (webpages visits, open and edit files, IM conversations etc) and shares this information across applications. While we can see it in action with Activity Journal Gnome-Shell extension this is the first time that Zeitgeist comes in the core Gnome.
This is how the contact list of Empathy 3.6 will look like and one goal is to unified online accounts under one “tab”, pretty much as Gnome-Contacts does. Zeitgeist is clearly used here by logging the contacts you talk most often and display them as favorites/top contacts.
While this is just a small paradigm of Zeitgeist, we might see it to work along with Nautilus enabling a more “semantic” way of looking for files.