I have no issues with the 'submit' button as-is. The expand button in the corner of the text area is everything I need, if I would type longer text and try to reread my writings before submitting them.

Post-preview is something that would make the people not read before they post, it's like that xkcd comic http://xkcd.com/481/ . Because of the fact that I continually reread my post, I mostly don't even post it, since it's not really contributing to the discussion. A positive effect, considering the goals of this forum.