An outbox would be pretty nice.
I still fall on the "don't send it unless you mean to send it" side, however. My outbox is only used when I don't have internet access.
Gmail just increased the time you have to "undo". Before the max was 10 seconds. Now you can choose up to 30 seconds.
When the feature first launched, I was worried I would eventually adjust to it, and stop re-reading emails before clicking "send". So far, that has not happened - it's effectively a psychological trick that continues to make my emails better proof-read.
