The faster response time, while not doing a whole lot to make an e-book a better device, does allow for embedded video and animation within text. An object or scene being described in text could be supported by an embedded visual application. Another technology the fast response time enables is digitizer input so the user can make annotations to the text.
One last benefit of the fast response time should be eradication of image persistance. I'd like to see more optical measurements, though, before rendering any comparison to an electrophoretic display.