I discovered the world of ebooks last night via Adobe Digital Editions software. For some time, our local library offered e-audiobooks and ebooks but we hadn't made the leap.
It took some time finagling before I "got" it. Now that it is all set up, we are allowed to "borrow" 5 books in this format.
Having never even seen a Kindle or a Sony Reader in person, I don't know what the difference is other than what I have set up is free but I have to read from my laptop.
I can live with the free and laptop part and not having to bring yet another device along with me.
We have 14 days to read our selections before it "disappears". If we are done early, we can "return" it. Amazingly cool! You can bookmark where you are and chose from a few display formats.
If you sign up for an Adobe ID, you can access your "books" from other computers, otherwise you stick with the one you are set up with.
When you are looking up books, if the number of licenced copies are all being used, you can place a hold and the library will email you when one comes up and will send a link for downloading.
If I remember correctly, you get a time limit to do so before the opportunity goes to the next person. I would highly recommend checking this out if your local library offer ebooks.