I like the idea of this. The ability to easily notify a user about a topic just by typing their name would be great. It would save time that would be required to PM them or find them on IRC or email to let them know.
I think that the @ should trigger an AJAX search of usernames as naderman described it. When parsed, it should simply be a link to the user's profile. To make it pretty, we could even color the user's username with their group color, but then again there could be problems with that if the user then changes groups and has a different username color.
Of course, we would need to keep it from re-notifying from within quote tags. And we should only allow a user to be mentioned once per post (and perhaps a limit on the number of total mentions per post, customizable via ACP?) so that people don't get spammed with mentions. I also agree with implementing a separate notifications area to house these and other notifications. If we cannot think of enough other ways to provide notifications for users, we could simply call it "mentions" and only notify users when they are mentioned.
Should users also be able to opt out of being mentioned? Some users might not want to be notified when someone tries to mention them. In such cases, users should be able to select a setting in the UCP and any time they are mentioned it can be parsed to link to their profile, but they don't get notified, IMO.




