One nice thing about the iPhone is that it renders italics and bold properly. I have come from Windows Mobile devices (and MS never really understood typography) where italics tended to be simulated (to save device memory) and generally looked awful. I was very pleased when some italics appeared in the book I was reading and it was "proper" italics.
It is great that eReader, BookShelf and Stanza are all being actively developed for the iPhone. As it stands eReader on the iPhone is already much better than it was on my Windows Mobile platform, it loads much faster, and doesn't crash if the device sleeps when eReader is running. I am very pleased so far...