In this very moment I'm sending a mail with three big photos to a friend. If you consider I don't have a fast connection (less than 2 mbps), it takes a while.
And then I was wondering: wouldn't it be great if after we click send it appears somewhere we can monitor its progress, but still use Gmail?
I know I can open another window, or compose from another window, but it will still be nice if sending mails felt more "immediate".
Probably with Google Wave we won't have this problem, but we are far from that now (and it's not mail, anyway).

Doesn't Offline Gmail allow this?

(My installation broke months ago – otherwise I would check and be sure.)

I can't imagine this getting implented when there is such an immediate work around – new tab, job done.

As Surly said, If you install Offline Gmail and enable "Flaky Connection Mode" then when you send the email it will be queued in the outbox and sent in the background.

Wow! I should have used a bit more offline gmail... Thank you! :D