I don't think the Kindle is in any danger of shutting down the ink-and-paper presses yet. 10% of sales, on Amazon, of books available electronically is a vanishingly small percentage of the market.
Now if you could rent books via the Kindle in the style of O'Reilly Safari, that could be a game-changer.
Reference books would be great for something like Kindle but with a more interactive interface. Being able to search and flip back and forth quickly between bookmarks would be great for reference. And the great thing about lots of kinds of reference? People will pay subscriptions for the kind that gets updated often! People will pay just to have information at their fingertips and not have to carry 3 or 4 thick volumes around.
Now if you could rent books via the Kindle in the style of O'Reilly Safari, that could be a game-changer.