People might say that it would be easy to type out the username of the person, but if you want to reply back to a larger amount of certain people it can be quite the hassle. Especially if the member has a long or mostly symbol username. I see this a lot on boards such as the CAAA where users mass-reply to one another. The mentions system would make it much more efficient.
Also people might say that quotes are about the same, but if you don't want to make your posts an unreadable mess you could use the mentions. It would clear up conversations and make replying to a lot of people easier.
It shouldn't be too hard to put into the code, since I'm very sure Nick wouldn't have a hard time coding it. It's not too horribly complicated and it will add a lot to the site, making peoples posts a lot more coherent and less cluttery.
Also, there should be a way to disable you from getting notifications, it would make everyone happy I think. I just like to personally know when someone is talking to me without having to search through the threads I'm on when I could know at the click of a button. I'm on so many different threads that I'm incredibly sure I miss some peoples replies to me and that makes me feel bad because I really do try to remember everything I reply on. And I'm sure there's many more people that post a lot more content.
Thanks for reading. Vote whether you agree or not in the poll above.
TL;DR Version
Argument: It would be too hard to code into CS.
Counter Argument: The CS forums are run on phpbb and they have an easy downloadable plugin for @ notifications. All that would probably needed to code is an area up by the "My Posts" Button. Site linked below.
https://www.phpbb.com
Argument: Since we can change our usernames it might cause issues with the system.
Counter Arguement: Each user has a specific code on this site. You can find it by going to your profile page. The number on the very end of your URL is your number. For example mine is 30130, the system will use this instead of your username to ping you.
Argument: I don't like pings.
Counter Argument: You might not like them, but many other users will find them helpful. Hopefully this system will allow you to disable them like how you can disable PM's.