GMail feature request: help me keep track of replies.

Scenario:

I sent out email to many people via BCC.
I get a bunch of replies to this email.
I want to reply in kind to these incoming messages, but GMail doesn't show which received messages I've replied to.

Suggestions:

Give the option of the standard threaded discussion via. While GMail's interface is better in most scenarios, there are cases where a tree is better.
At minimum, give some indication that I've replied to a message. With many messages stacked in a thread, I can't figure out which I've replied to and which I haven't.

You have until next Friday, or I'm going back to Hotmail.

I bet if I wait long enough, Microsoft will give me $.05 for every email I send.