New functionality - if you want to mention someone in your post, you enter the @ sign and immediately followed by the username you want to mention, you will then see a list of names popup on your screen from which you can choose. The user you mentioned in your post will receive a notification by email that his name is being mentioned.
As a reminder, please update the email address in your account. @mention functionality will not work unless the email address in your account is valid.
This functionality is the same as what you would do on Facebook.