The above tools serve to keep notes and files. Nevertheless I continue to use e-mail as an archiving tool because: - it pops up unread in my inbox for later processing. If I want to use it on a specific device, I can just leave it unread until I have access to the right device. - more importantly, email is ubiquitous, and I can have somebody else email me a file.
I still need convincing on what problem Hopper solves for me that the other tools don't. That said, trivially easy drag-and-drop file storing is cool, and I for one welcome our so-simple-my-grandma-can-use-it usability overlords.