Add "@" user tags in forum
Add parsing for the "@user" formulae like on Twitter and parse it when the user posts a message, to send a notification to the user referenced in the post.
The message (e-mail and profile message) should say:
[User that referenced him] has mentioned you in a forum post on [Campus URL], in course [Course title], forum [Forum title]. To check the message, go to [direct URL to the forum]. If you are not connected anymore, you might be asked to login again in order to see it.
It should not be dependent on the "forum notification" option, as these notifications will always get to you for any message (including those in which you are mentioned).
No message should get to you if you do not have access to the forum itself.
The message should use the messaging API and not be sent directly if there is a delayed process (cron).