Some folks notice that my email style is slightly different from the dominant paradigm. In particular, my email is sent as plain text with hard carriage returns. This puts me in the league of internet graybeards who developed their on-line habits with USENET before the web was invented.
My email replies use the in-line style of replies. Jon Gruber provides a succinct explanation why the dominant form of quoting the entire message and top-posting the reply is not helpful. And while there is a variety of opinions on the subject, I understand that I am clearly in the minority, and talking to the wind.
I don't mean to be obnoxious, but I thought it would help to know why it seems like I'm mangling your email. The original netiquette article, Netiquette Guidelines (RFC 1855), has this to say
Be brief without being overly terse. When replying to a message, include enough original material to be understood but no more. It is extremely bad form to simply reply to a message by including all the previous message: edit out all the irrelevant material.
It is easy to get into a debate about netiquette. While acknowledging the risk of being misunderstood, my position is that on-line communication (via email, forums, blogs, etc.) is more effective when the cruft from a quoted message is deleted. By deleting all the unnecessary part of your message, I'm trying to focus your attention on just that part of your message that prompted my reply.
Occasionally I revert to the top-posting form, especially when I don't want to confuse a long thread involving multiple people who have been using top-posting.