tl;dr

Top posting annoys me, and here’s why. This was originally written for Usenet but applies equally to email and indeed the hip new forums all the kids are talking about these days.
=================== begin generic top-posting cuss ==================
Regarding top-posting:

1) Some quoting is necessary. This has to be done in order to give  context to your reply. Remember that it might have been several days since the viewer has read the original article you are replying to, and  due to the vagaries of NNTP propagation, he (or she, naturally) might not have read it at all. Some quoting is therefore necessary. This also ensures each article is readable as it stands, without reference to previous articles the poster might (or might not) have read. Depending on the nature of the article being replied to, some or most of it might be quoted. Signatures should always be removed, and you can choose to indicate the removal of other text by inserting the word {snip}.

2) Having decided to quote, it dramatically improves the readability and flow of your document to intersperse quote and reply in the manner usually adopted on most newsgroups. Top-posting means that anyone trying to read your article as a free-standing document must scroll up and down, trying to figure out who said what and to whom. It implicitly carries the message that "my time as an author is worth more than yours as a reader" and so offends people. It takes seconds to compose a properly trimmed and quoted reply. Please do so.

Remember that Usenet is very, very old indeed in computer terms. These  rules of netiquette have evolved over that time, and although they may look odd, there are very good reasons behind them.

Finally, it is true that many newsgroups accept top-posting. When I am in one of those newsgroups, I respect that convention, and I do not cuss people for top-posting. This newsgroup is one of the ones that does *not* tolerate it, and I would ask you to extend us the common courtesy of respecting our conventions when in our newsgroup.

For further discussion on this matter, please see
http://www.geocities.com/nnqweb/nquote.html and
http://www.malibutelecom.com/yucca/usenet/brox.html
which have some other arguments. If you wish to read more,
http://www.google.com/search?q=usenet+netiquette+top-posting
has plenty of suggestions.

In short, please don't top-post.
=================== end generic top-posting cuss ==================

Personal