The keyboard is still one of (the?) most efficient mechanisms for interacting with a computer. Many applications that aren't text-entry centric can increase user productivity by using keyboard shortcuts for functionality (think of a video editing application: fast-forward, back up 2 sec, mark a segment, etc...). However these function suffer greatly from discoverability issues. If you could put the functions directly on the keyboard, you'd be able to find these shortcuts much faster, and be able to be more productive. Once you've learned the shortcuts, the e-ink becomes less useful, but during that initial discovery (and memorization) phase, it would be extremely helpful.