Well, neither can you resize and reflow text on a paper book, but it's great to have available on the Sony Reader! ;-)
But I agree with what I take away from your comment... simplicity is paramount, and all of our wishlist items need to be balanced out with whether or not they take away from the simplicity and effectiveness of the book paradigm.
That's why they pay the Sony folks the big bucks -- they have to make those tough choices and live under real product design constraints. As a consumer, I don't have to be practical, and have the freedom to give them long lists of wistful ideas!
