The Problem
In comments, when someone's username is mentioned in comments (e.g., @applemonkey496), it does not seem to give any indication that the mention worked, and that the user was notified. Furthermore, if someone's username is spelled incorrectly and therefore doesn't work, there is no indication of that either. For example, "@applemonkey495" will be styled the same as "@applemonkey496" even though one of them works and the other does not.
Proposed Solution
When a user is mentioned, the name could be written in bold or even linking to the user's profile:
@applemonkey496 or @applemonkey496
@\w+
s in a classy span, and slapping some style onto it, shouldn't be hard.@<name>
comments should link to the named person’s profile (like Twitter). “[…] linking to the user’s profile” — wouldn’t linking to a specific comment make more sense? And if this gets implemented at some point in the future, this probably won’t be automatically applied to all comments retroactively, because this would likely involve the performance overhead of automatically formatting all comments in the database.