We are in the midst of creating the Social function of the search engine.
1) We created the "Popular" functionality on the Search.
2) When "Popular" is clicked, the page results shows up and it shows the search results based on how much activity (comments) each one has.
3) We also made it possible for users to choose a category for content they want to save directly from the search results page.
4) When a user doesn't have any categories yet, then two defaults categories are created and shown for him: Review Later, Favorites. The user can go to his Saved Categories and rename these, or add other categories. If the user has updated his categories (renamed, removed, added more categories), then his/her categories are shown immediately after clicking on the Save button.