I would suggest typing the up and down arrows at the bottom to two keys, j and k would be appropriate. Then have the mouse-overs for those buttons include the keyboard shortcuts. Yes, you can accomplish the same thing with spacebar and arrow keys, but it is annoying to jump to a spot halfway through a slide then have to scroll.

The functionality is already there. But I personally don't like to have to aim my mouse to navigate when I'm reading a long document.

Another idea to consider is creating an iframe version of the page, which would allow you something closer to the old experience. The nice thing about that is to allow third party websites to transparently embed scribd documents in their pages.

Other than that it looks good and is more pleasant for me than your flash interface.