I want to respond to cerement's signature that says, "To manufacturers: Design an ebook reader for readers that focuses on design and typography."
I wholeheartedly agree with that one! Reading and books is not just about plain text. Plain text is the reason I shy away from .HTML files for digital readers. Typography and book design and layout is very important. Because of that, I generally favour formats that are Adobe Digital Editions or Adobe PDFs or variants thereof because they are not only concerned with plain text but also design and layout.
In fact, I find the whole business of being able to change the font of a digital book to whatever you want rather "insulting".
Okay, said in jest. But, the fact that some digital formats allow us to change to any fonts willy-nilly is suggesting that design and layout is merely secondary to plain text. Not so. Communication happens not just through text but through design and so forth.