Marco Arment on iBooks and private APIs:

I won’t be able to offer some features that iBooks has (such as a true brightness control), but my customers will expect them, making my app inferior to Apple’s in key areas.

Assuming you want to build an app, that is. Seems there’s two ways onto the iPad at the moment – either a) you upload an ePub ebook onto the iBook Store, or you build your own book/reader app. Will have to wait to see which of the two is better.