Facebook announced today that it is allowing users to create and click on hashtags, “similar to other services like Instagram, Twitter, Tumblr, or Pinterest.” A hashtag, which is simply a word preceded by a pound or hash symbol (#) is a way to participate in a public discussion about a topic and allow others to click on or search for the hashtag to find your content. Google+ also hashtags.
Access depends on privacy settings
As with all posts on Facebook, someone’s ability to see what you post (even if you add a hashtag) depends on the who you’ve agreed to share the post with.  So, if you share a post only with friends, then only they will see it If you wish it to be seen by anyone you should click on the little icon below the post and select Public.
Hashtags are clickable and searchable.  I tested it by searching for #NSA and, as I expected, I immediately found posts from friends and even strangers (who had posted to the public) about Natonal Security Agency surveillance tactics.
According to Facebook you can now:
Search for a specific hashtag from your search bar. For example, #NBAFinals.
Click on hashtags that originate on other services, such as Instagram.
Compose posts directly from the hashtag feed and search results.
(Source: Facebook)
Implications for sharing
Although this is a little change, it has big implications because, with hashtags, Facebook pages can become part of broader conversations.  While it’s certainly possible to use hashtags mainly to share stories among your friends, they encourage users to share more broadly as is customary on Twitter (where the vast majority of users post to the public). One difference between Facebook and Twitter is that Facebook allows you to determine the audience for each post each time you post so it’s pretty easy to have some posts shared with the public and others shared only with friends or friends of friends.
http://www.forbes.com/sites/larrymagid/2013/06/12/facebook-adds-twitter-like-hashtags/?utm_campaign=forbestwittersf&utm_source=twitter&utm_medium=social

This is wonderful.