Clocks and supply are already gated for chips to conserve power. Also different parts of the chip work at different voltages to conserve power. You'll find that now it's the display that makes the major difference. Yes there is still room for improvement in chip design, and that's why I have a job. Newer chips will keep getting better in terms of efficiency.
Coming back to displays, this tech is something that I've been waiting for. A colour reader that can last for a couple of weeks would be awesome.
My wish list:
Colour screen with a resolution of 1280x800 for reading technical papers
Battery that can last at least a week
Wi-fi, bluetooth, usb (3G would be nice to have)
MP3/OGG player (FM radio would be nice)
Pop/imap/exchange client for email
Support for pdf, epub, doc, xls, ppt, images,....
Touch screen with a pen for scribbling notes