I believe this marks the biggest change in Ubuntu's history. More-so Canonical's. Taking a leap forward without knowing exactly what Unity could do to their reputation, and still giving it a shot. It takes much effort to put forward your vision. The vision however, may not be seen as soon as it is revealed, but may instead take a little longer to settle in.
A few months ago I wrote that Ubuntu should hit the shelves. Due to Unity being a big hop, why not? Since it's such a swift turn in direction from other streamline distributions, it's the best time to throw it out there. People in the store would know Ubuntu as Unity, not straight-forward GNOME. This, I believe, would be a natural come-to for new-comers to Ubuntu, and Linux in general. Get them used to it as Unity and stick with it.
As it is, there is a "Files & Folders" icon that you can click on and proceed to a folder. When you click on this folder it opens up a file browser (Nautilus) - This should be changed and allow you to navigate through folders within that area. Much like Nautilus, this icon should also allow you to point at a music file and it starts playing - Or you can right click it, and select "Play," "Add to Queue," or something else that would be suitable such as: "Sync," or "Push." Basically, the entire "Unity" experience needs or should be integrated into Ubuntu One. It shouldn't be forced onto the user, but should be there/exposed for convenience.
This is an outegration that is a downside to the clutter-free / seamless environment. It by default, should be an integration.
This is not a review. Just a "some things I'd change" post. I have not used it long enough to give any final passing-thoughts. I feel that this is a big relocate-move for Ubuntu, and it's still too touchy to be able to lay a final piece out.
Edit: I removed the "Social Layer" bit due to this already being available when you click on your own username. I was thinking something slightly different, but this works practically the same way. (being able to easily post updates to networks)