Twitter's official clients on some platforms (iOS, OSX) invert the scroll direction when reading DMs and @replies from a specific person. Is this the best UX in your opinion, or is it just confusing? How should it work?
When reading public tweets, or looking at a list of people who have DM or replied to you, the latest message appears at the top. This model is followed on the Twitter website for DMs and @replies.
On iOS and OSX, when viewing the most recent DMs or @replies from a specific person the latest message appears at the bottom. This differs from the rest of the UI but is familiar from IRC/IM/whatever chat: read top to bottom.
I can understand the arguments for both approaches, but for me it seems like there's a disconnect in the interface when the approach is inverted dependent on platform  and app screen.
 I don't know how Twitter behaves on other platforms, but on my Android device's client (presumably official because it has a proper Twitter logo), @replies and DMs are latest-at-top.