I found the most information about both NetLibrary and YPL's Digital Books by going to the Help pages. NetLibrary has a really great Demo from www.oclc.org.--nicely paced and very informative. Digital Books also has a good easy to read Quick Start Guide.
Both have so many thing to see. NetLibrary has many ebooks--from the Demo, other subscriptions to NetLibrary also have audiobooks and ejournals. There are quite a few language options. The books cover any topic I could think of. It's very easy to use and has a nice format. You can read the books right on your computer.
Digital Books also has wide variety of books and audiobooks to choose. Their books must be downloaded--you cannot just open them up on the screen like NetLibrary.
The advance search options on both are very versatile. I like all the different options you have for searching.
I can definitely see the uses for ebooks and audiobooks. It's great to have something you can access anywhere in the world as long as you can get to a computer and have the necessary devices for reading/listening to the material. With ebooks, particularly, it's nice to be able to search within a book for certain keywords if you can't remember where you read something before and the index isn't helping you. I don't know if I will ever actually use audiobooks for myself, though, as they tend to put me to sleep. I'll use the MP3 player mostly for music.
I'm including a link to the original PLCMC lesson, mainly because I like have a link to each of their lessons in my blog.