I keep meaning to do some sort of comprehensive post on e-books. And then other people keep doing such a great job of it.
JA Konrath talks about why he prefers to borrow his son's Ipod Touch to buying a Kindle right now. (He also has a number of posts about the success of ebooks and pricing.)
Sasha White talks about how her e-books outsold her print books by a lot.
Lynn Viehl has a great post talking about how e-books are often the cheapest marketing an author can get.
Even Jennifer Blake (who was one of the first authors I was aware of putting her backlist in e-format) also talked a little about it.
Smart Bitches have some discussions (including a response from a publisher) about the timing of releasing the e-format. The response from one publisher is an interesting point, since they feel that the comparison to music is unfair since Publishing has traditionally used a Hardback to paperback transition and they feel selling the e-book at the same time is akin to releasing the paperback at the same time as the hardback.
Now, I don't entirely agree since, as commenters there pointed out, and as was brought up over here in Dear Author, when you buy an e-book you do not have the same rights (if you will) as a hard copy - wither hardback or paperback. You are buying the right to view the content. In many cases you can even view the content in a few places - multiple readers, your laptop, and so on. (I believe mobi-pocket limits it to four. I'm sure they are not the only ones.) However, if you change readers and your content is not readable on your new reader, you have to buy a new copy. (Much like trying to play a tape in a CD player, sometimes it just can't be done.) Now some formats span multiple readers, but none are currently workable on all readers. (I point you here to Fictionwise's site for a sampling.)
Also, if I read something want to give it to a friend, sell it on ebay, or mail it to my aunt - I can only do that with a hard copy. I cannot transfer my e-books to someone else. (This is one reason I'm not surprised publishing hasn't jumped on this more. Considering the number of authors I heard complain about people buying their series from a used book store only to be surprised that the publisher didn't renew the contract. Well, e-books solve that.)
And, if they decide that oops, we gave you that for free by accident, the company can sneak into your device and take it back.
So, why would anyone ever buy an e-book then. Well, I for one, love having, say, seventy books in one tiny compact device that fits in my purse. It helps with some of my storage issues. I love buying a book on the day of release even when my day does not really allow me to get to the bookstore.
I love having backups of my shelves online. (Yes, that hardly matters if I change readers, but I still like it.) It means my e-books, while locked into the format I purchased them in, are available to me even if I destroy my device or lose it. (Ask me how I know.)
I haven't stopped getting actual books. And I don't know that I ever entirely will. Certainly it's fun getting books signed and you can't really do that with e-books. But I never was one to lug my entire backlist to get it signed anyway. I was always happy with a few.