The scribd link appears anytime you submit a PDF directly. This was/is useful for people who hate downloading PDFs, since scribd does not require this. Of course, a lot of us (myself included) use Chrome, which allows you to open PDFs inline...
From what I remember, the scribd side is even flakier than opening a PDF in your browser. And I'm not too keen on this "push our dogfood on readers" policy, either...
