No doubt by now you've noticed that many of the "applications" available on the iTunes App Store are various ebooks by AppEngines (iTunes Link). I thought I'd take a look so you can see what you're getting for $0.99. Each of these applications is a single classic (and thus copyright-free) book. For my tests I chose Jane Austen's delightful comedy of manners, Emma (iTunes link).
When you first open one of the AppEngines ebooks you get a nice "leather" cover splash screen with the name of the book. Then you're taken to the first "page." You can advance pages by either swiping (right to left) or merely by tapping the screen. You can go back a page by swiping in the other direction. There are three font sizes which you can choose via the pinch gesture.
At the top there are two buttons: a table of contents button that lists chapter titles and a search button that allows you to search for text. When you search on a term, it is highlighted in yellow throughout the text. Unfortunately, as far as I can tell there does not seem to be an easy way to move to the next instance of the search term. You just have to page through the book until you see the next highlight.
While there are several book reader applications in the App Store for both commercial (i.e DRM-ed) and open-source texts, I think the AppEngines editions are basically worth the modest purchase price for the convenience. Personally, I find it nice to have separate home screen buttons for each book, and the presentation is more than adequate. Be sure to check out the gallery below.