The sequel of this post, it's now fully working.
It's all made in CSS2, there is no images (the icons are edited versions of Nicolas Gallagher's ones) and in plain JS.
I used the FileReader API to preview the file, so the previewed file (if it's an image) works as a progress bar (well, there is a <progress> bar but more is better).
A also used the webkitNotifications API which pop out when the file is uploaded. I really like this API I don't understand why it's not in the spec.
All the animations are done in CSS3 too.

Works only in Chrome and Firefox.