It will now alert you if someone makes a comment like:
"@Tom did you know that..."
It either needs an EXACT match with the , or if no exact match is found it finds an exact starting match on what was entered, for example if there was a user:
And you entered:
It would match SpaceMan2000. This feature isn't on the forum yet, just sitewide comments but it will be on the forum eventually. Also it should be noted, you can't notify someone who hasn't posted in the comment thread! If I haven't left a comment in that particular string of comments, Tom won't notify me.