Actually, iBooks syncs between my iPad and iPhone for
all books!! - I've never bought a book through the Apple bookstore, but I can close a (de-drm'd epub) book I've added through iTunes on the iPad, and open it on the same page on the iPhone (a 3G)
This is really good news - and one up on Amazon!! In fact, it may have convinced me to upgrade to the next iphone - was looking at moving to Android
(Only tried epub though, don't know about anything else)