As somebody who has a shitload of books taking up physical space, and who usually requires 3 or 4 books to get through a business trip (depending on how long the plane ride is), I'm all set with the concept of a file I can take around that will not take up space at my house or add weight to my bag and be instantly searchable.
However, I've also found today's reading technologies suffer due to display quality, so, ehh, forget it, mostly. I have bought a couple for my Palm just to see how I liked it, and again, the display--just not good enough. When we have 300dpi electronic paper I have no doubt it will be a killer app!!
Having said that, for an interesting ebook business model, check out the Webscriptions at Baen Books (
www.baen.com). There is a free section, and even in the paid section, most of the books have at least one chapter up for free so you can see if you feel like paying for it.