I know its unusual but Ive seen a feature I love in another webmail. AUTO BCC and I type an address, such as mine. This way, all emails I sent I get a copy, so I can store them, move them to some other folder. This way I dont have to BCC myself manually and type my email address each email I sent.
Anyway, if you dont like this idea, perhaps when GO has threading, it might be a solution for me. Some webmails like Afterlogic, when you reply an email, automatically your reply is threaded with the original email you received, which is nice too.