3) Cost: E-books are significantly cheaper than most printed editions, esp. for books no longer available.
Significantly? My experience has been that for a "recent" single novel eBook, you usually save about $1 off the paperback price. (I will grant that savings for TPs and HCs are often a little more substantial.)
And as for older out-of-print books... whenever I go looking for a specific book, I usually tend to find it is not available. I was hoping that I would be able to get more OOP books this way, but I guess perhaps the publishers feel the effort to digitize more obscure older books isn't worth it?