It would probably be most useful if it didnt have the @ in front of the username.
That way if person x was talking about person y.... then person y would be getting an alert telling him folks are bandying his name around.
Facebook handles it by typing @name in your status and then you're given a dropdown to select whoever you want to mention. When you you select someone it turns into their name and is linked to their profile. I'm sure they also get an alert about it too.
If this were implemented here it could be something similar.