I've been doing it longer than that, but I don't quite agree that "it's the only right way". I top-post maybe half the time now, depending on the kind of reply

I've been doing it longer than that, but I don't quite agree that "it's the only right way". I top-post maybe half the time now, depending on the kind of reply (as you note) but also my audience's expectations. For example, when replying to a developer list for an open-source project, I'll usually use interleaving because it's the style in that community. In business contexts I'm more likely to top-post because that's what everyone else does (and as another poster noted, Outlook is broken). I guess we don't disagree too much; I'm just saying I don't try to force interleaving where it's not likely to be appreciated.