I'd say that that's what preview is for.I think there needs to be a time limit, perhaps.
I will say things, hit submit. Then re-read and then it looks/sounds different than what I wanted it to. So I go back and change it.
How about a full edit log?
You're allowed to edit old posts. But diffs will be saved, and each edited post have a link to the full revision history. I think that woud be a cool feature.