I wish I could find the article I read that quoted a study that showed that people tend to increase their purchasing of physical books once they start using an e-reader. I work at a used bookstore (yes, they do exist, and many are doing quite well, thank you) and I can't recall anyone coming in to sell off all of their books because they are replacing them with electronic copies. Most folks continue to sell them for the same reasons they always have : because they are moving and need to shed the weight of books, because they inherited a lot of books, because they are going through some life-changing event (kids moving out, divorce, etc) but mainly they do it so that they can make room for more books. However, when I used to work at a record store, I had lots of folks selling off their CD collections because they had ripped all the tracks & now found the actual physical copies a nuisance. People didn't need to keep those shiny silver platters, but they do like to keep books around.