Well, I'm almost through this experience.
I tried to download some audiobooks using a couple different sites. My main reaction is that we have to perfect the technology before this is widely used (I need to get a new computer which I'm in the process of doing!) In general, it takes too long to download the books and there is no standard technology yet. I'm still looking into audiobook services offered through Califa, the California state library consortium. I know they offer special rates on subscriptions to eBooks but when I last looked the emphasis was still too much on recent best-sellers. I am more than happy to look up a title for a student (and hopefully encourage them to do the same on their own) to see if it's available through the public library system.
I'm also still a skeptic about textual eBooks (pdf or html). Next year I am going to have a school subscription to Questia which includes thousands of eBooks and I'm going to be able to get a better sense of how students use the texts. My hypothesis is that they will use eBooks in much the same way they use print books, taking snippets of information from here or there in a book. Of course, they can't really cut-and-paste with print materials.
BTW, speaking of really useful materials, we have so many e-materials available these days that the challenge is, like with everything we do, getting the info into the user's "hands." That's why I catalog every issue of CQ Researcher, every issue of Congressional digest and its siblings. The kids find them doing keyword or subject searches in the catalog and then are able to log on to the database and find the article online. A tremendous resource but it won't "sell" itself!
Last post coming!