If there was both a From: and a Reply-To: header then the hash could be added in the Reply-To: which would leave the From: header non-ugly (maybe even set to the posters address, but that's another topic).
I wonder what happens to the Reply-To: header when an email is forwarded - maybe it even gets discarded by most mail programs which would be nice in this case. I just tested it with mutt: it discards the Reply-To: header.
Another issue, propably solvable with a smart regex, would be the ignorant full-quote-at-the-bottom that many people just seem unable to avoid, and which would just look terrible in a forum.
I agree with Ben that openacs.org is the wrong place to try this out, though. Maybe it should never be enabled for the public site, but this functionality certainly makes sense in other settings, e.g. an intranet that consists of trusted users only.
