> Here it's quite obvious who you're responding to, because your comment is indented under the comment you've replied to.

Right now that's indeed true. If later on there were to be a lot of intervening comments, it'd be more difficult to tell immediately who the response was directed to. In that case, the @name convention likely would be helpful to readers.

> Also, while we're at it, replies that say no more than "I agree" or "I disagree" are generally frowned on here, since they're almost completely contentless and don't contribute to the discussion.

That's certainly true in the general case, when you have a random third party chiming in with his or her agreement.

In this case, though, the "I agree" was a useful clarification: It signaled, to someone who had responded to me with what could be interpreted as a challenge, that we were on the same page.