Let's start with a "back" button in the e-reader, to take you back to where you just came from. Every time I've clicked on a link in an ebook and it takes me to an earlier/later spot, there's no easy way to go back. (Note: Regarding the back button, I'm talking specifically about the iBooks reader on the iPad.) Or how about when you're in the index and you click on an entry, hop to it but it's not what you were looking for? You're stuck on that page and you have to manually find your spot back in the index again. Imagine a web browser without a back button. Pretty awful, right? So why do we have to live with e-readers without back buttons?
How about pop-up windows? Why are all the popular reading apps typically built with just a single window in mind? Imagine how frustrated and less efficient your day would be if your computer only let you open one window! In the index, if I press and hold an entry, show me a preview of where I'll be taken if I make that selection. It's the same concept I use all the time in my Bing search results, so that I can preview where I'm heading before I leave the current page.
And how about similar functionality in the body of the book? Press and hold a word or phrase and you get a list of related entries and "see also's" from the index. For example, let's say I'm reading the "Get Online" chapter of iPad: The Missing Manual and I see the term "3G". If I press and hold it in my iPad ebook reader there should be a list of links to where 3G is first defined in the book. But there should also be links to where related topics are covered, such as AT&T, cellular network and even wifi, so that I can understand the difference.
Next, similar to pop-ups, why not let me have a split view into the book, or, heaven forbid, allow me to have two books open at the same time, both visible on the screen, one using the top half and the other using the bottom; these are basic features we take for granted in apps like Word or Excel but they're nonexistent in the ebook app world.The index is such a critical element of a print book and it could take on so much more functionality in ebooks. Which reader app will be the first to enable these types of enhancements? I'm not particularly loyal to any one of them, so I just hope at least one of them offers these features sooner rather than later.