In my application, I want to notify a user, when he/she is mentioned in a comment or a post.
The user handle is @user_name
, similar to Facebook
I actually am interested in a concrete answer to this myself. I don't know how Facebook and Twitter do it, but I do know from general searches that the gem acts-as-taggable-on could get the job done. Check out https://github.com/mbleigh/acts-as-taggable-on.
Also, this question on stackoverflow might also provide you with some info: Implementing twitter-like hashtag on rails
Good luck. I encourage you to try to get more attention to this question and get a more solid answer than what I've said. :]