I looked through the world book fair site and at first glance did not get excited about it. Then I looked at the collections list and was fairly impressed. Then... I found out you have to be a member (small $) to use the collections section and was not so impressed. Here are some examples of the variety of the collections:
BuddhaNet , BuddhaNet™ is the result of a vision to link up with the growing worldwide culture of people committed to the Buddha's teachings and lifestyle, as an on-line cyber sangha.
The Public Domain Music Score Library attempts to create a virtual library containing all public domain musical scores, as well as scores from composers who are willing to share their music with the world without charge. Since its launch on in 2006, more than 17,000 scores by over 1,000 composers have been uploaded, making it one of the largest public domain music score collections on the web.
Children's Literature Collection is compiled from scans of original image rich children's books. The World Public Library Children's Literature Collection is a selected list of the most popular children's books of all times.
LibriVox is a great resource for those looking for audiobooks. The reading is done by volunteers, so I do not know about the audio quality. I know I will be showing this resource to students when they are doing literature units.
There are a couple of advantages to ebooks like text searching, the ability to change font size and they maybe more environmentally sound. But... I personally would rather have a paper book. They don't need power, they are better on my eyes, and... they just smell right.