I think we need all email application designers to sign-on to this idea: Prevent users from typing their whole message in the subject line. I'm picturing something like the dreaded Clippy popping up to say something like, "You appear to be typing an awful lot of words into the subject line. Would you like me to copy this to the body of the email instead?" The help system could then further explain that the subject line is a brief summary of what the email is about while the meat of the message is contained in the body. Perhaps it could also point out that people that put more words in the subject line than there are in the body of the message are more likely to annoy those on the other end.

Or maybe I'm just crazy.