Indenting and maybe vertical lines to help the reader figure out the threading would be an improvement. However, I don't think this is good enough in a long ema

Indenting and maybe vertical lines to help the reader figure out the threading would be an improvement. However, I don't think this is good enough in a long email chain. The way traditional email readers solve this is, of course, is with two views, one of threaded email subject and another for contents (http://www.davep.org/mutt/screenshots/ http://www.davep.org/mutt/screenshots/). I don't think gmail will ever adopt this interface, though.