This will bring true portability to books purchased from the Sony ebook store.
I haven't had a chance to test the ePub format, so can't predict if it will become the MP3 of reading. And since we already had some pretty good open source text formats anyway, I remain suspicious of the whole thing. Still, I can hope this move will pressure Amazon and others away from the suicidal path they have set ebooks on. There has never been anything about the codex that prevents you from passing one along to a friend, xeroxing it, or even scanning it into your computer and translating it to some super-portable format like PDF or Open Office. Book sales may not be what publishers would like, but it doesn't seem that my ability to scan my book and then read it on my Kindle is doing substantive damage to publishers' profits.
If publishers and sellers will agree upon a truly open, standard format, I will purchase far more ebooks in addition to the large number of hard copies I will continue to buy every year. They need customers like me. I can be readily replicated.