Teleread has a great post in which the author reports on his/her experiences with the Sony PRS-505 ebook reader after one year of use. I particularly wanted to point out the section of the review entitled "Have my book-buying habits changed?" because it mirrors my experience reading and buying books for the iPhone. I used to get almost all my reading materials from Calgary Public Library, but in the past 8 months or so that's changed as I've bought all of my leisure reading on sale from Fictionwise, and almost exclusively for the convenience factor. The frequent sales entice me to buy the books I want, and in some cases books I was waffling on just because the price is right and the buying experience is so easy.
So to summarize for the publishers: Before ebooks I didn't buy. After ebooks I buy.