If you go to a Drupal project page (example Views) you will see a new button with a Start like this:
And you can Star and Unstar a project, but what is the real use of this button?
I can't find all the users that have starred a project.
Consider this "Star"-facility as a way to "bookmark" specific contributed modules as your "favorites". Some more details about it (from What’s new on Drupal.org? - April 2017):
Users on Drupal.org may now star their favorite projects - making it easier to find favorite modules and themes for future projects, and giving maintainers a new dimension of feedback to judge their project's popularity. Users can find a list of the projects they've starred on the user profile. Over time we'll begin to factor the number of star's into a project's ranking in search results.
For the moment the only thing that I can remark is a list with your starred projects, this is available in your profile:
And you can access trough https://www.drupal.org/user/YOUR_USERNAME/starred