I've been using Scratch (great app by the way), and noticed this when I linked it to my Dropbox. The usual flow for this type of OAuth is to show a webview -- either in the app or in Safari -- where the user has to log in and allow access, which then redirects back to the app.
Scratch has a similar flow, but instead directs the user to the Dropbox app where they can allow or deny access:
This may seem like a minor difference, but it's a much nicer experience. Having to enter your username and password can be a huge pain on iOS, especially if you have a really complex password. Skipping that is a big win.