How do you reply in e-mail?

Erik and I are of like mind when it comes to e-mail replies. Unless my reply is one sentence or less, I never top-post. After all, it is common sense to reply within the relevant portions of an e-mail, especially if the e-mail is long and/or covering multiple topics.
So if it’s common sense, it only stands to reason that millions of Internet users have been trained by Microsoft and other software vendors in to top-posting. Grrrrr….