There's no doubting that if ePub gets widely adopted it will be an enormous step forward, allowing you to easily take books from one reader to another and providing a much better experience. In fact it has almost convinced me to pony up the cash and get a PRS-505 shipped over from the US for me, now that I'll be able to buy books from a variety of sources on it.
I am curious though to see how it handles inline images and things like decorative first letters at the start of a chapter. These things are probably going to take a little while to find out while people start playing with the format more.