Wow, the thread has definitely exploded
Thank you all for your opinions - I'll definitely store the .epub files as back-ups.
On the formatting front, I think that most current ebooks don't look as nice as pbooks, but for most texts I don't care. I agree with rogue_ronin though - text files with paragraphs broken in lines (like the Project Gutenberg example) are really annoying. I can stand the lack of italic/bold/fancy lettering, but standard-sized lines are awful - what if I want to use a bigger font ?