THE HUNGER GROWS.
About 5% of top firms let applicants know when a job is filled. Common decency should demand, however, that even in a large search, a mass-mailing to all applicants should be the rule. And the top three finalists should get personalized feedback; they could be your top candidates in another search so you want to keep them happy.
A candidate performance review that helps rejects learn what they did right and wrong is essential for internal candidates because they are inclined to leave if they don't see a future with the firm and a rejected promotion is often taken to be the indication of a dead end.
And, indeed, any head-hunter would surely profit by sending a thank you email to everyone she has spoken to in the course of a search, letting them know that the job has been filled. It takes time away from money making projects but it strengthens your network and it's great advertisting too.
Reference: Yves Lermusi, ERE