I've written about some cool iPad book apps before, specifically vBookz and The Pedlar Lady of Gushing Cross. Both apps are great examples of why the iPad is more than just a big iPod touch. The large screen makes it practical to view books with more than a paragraph displayed at a time.
Now, those iPad book apps have been 'downsized' to fit on the iPhone screen. Did it work? Well, yes, in these cases. First, the appeal of vBookz is the text-to-speech capability, so the focus is not on simply reading the text on the screen. And the appeal of Pedlar Lady is the beautiful animations and again the audio narration. So while the fonts are small or there may be more pages to present the same material, it's the audio that makes these particular iPad apps translate well to the small screen. That may not be true for traditional text-based eBooks but it works for these apps.
vBookz is a universal app so your $1.99 purchase works on all iOS devices and you can download 30,000 additional books for free. Additional languages can be purchased in-app. The Pedlar Lady app is not a universal app, which means the iPad and iPhone versions are separate and each priced at $4.99.