Since one can make posts public, is it possible to search for say, all users who mentioned Ponies in their posts? Specifically I am looking for people who have posts pertaining to My Little Pony
Search Google Plus Public Posts
google plus
You can use the Search box in Google Plus. It's just to the right of the Stream/Photos/Circles/etc. bar.https://plus.google.com/s/Ponies You can further refine the search to just posts (in your circles and public posts) https://plus.google.com/s/Ponies/postsDon't forget to use Best of / Most recent per your needs.