Chris Hanson describes the One True Quoting Style. He's completely right. One of the many reasons why I use Eudora at home is because it lets me write email exactly as Chris describes it.
Naturally, it's completely impossible to get Outlook to do quoting this way, so nobody at work snips the text they're replying to and inline replies are extremely rare. I suppose I'll end up using Mail at Apple -- I wonder if it can be coerced into behaving correctly. As far as I can tell it can come close, but it inserts an extra line at the top of a reply and puts the starting position of the cursor at the beginning of that line. I'd much rather the cursor start at the bottom, below the quoted text, or that all of the quoted text be selected (as it is in Eudora). The extra line is annoying.