I’ll heartily second what Jim Fallows says here (though without rehashing my earlier anti-Kindle thoughts, I wouldn’t say it’s an argument for the Kindle per se so much as eReaders in general):
My main view on communications media is that new systems usually add to old ones, rather than displacing them. Radio didn’t eliminate books and newspapers — that would come later!; movies didn’t eliminate still photos; TV didn’t eliminate either movies or radio; and the internet has not (yet) eliminated TV. A few communications systems do disappear altogether, except for specialist/curio use: vinyl records, photos on real film, etc. Usually the field just becomes more crowded and the options more diverse.
So it will be, at least for a while, with e-readers like the Kindle versus “real” books.
To add to this a bit, what I think this kind of innovation in new communications channels does is to rationalize the kind of content on each. For all the nostalgia that some (e.g., me) have about obsolete forms, books do a better job at holding novels than newspapers, so we don’t see serialized novels anymore. Similarly, TV and movies do a better job at dramatic narrative than radio, so very few radio dramas still exist. But radio’s still excellent at talk shows and sports broadcasts (safer, too, if you’re driving), and the nature of the technology means that nowadays we can shove a radio into just about anything else (e.g., cell phones).
eReaders are going to perform a similar function – eventually (sooner than later) they will mostly eliminate the printing of many academic texts and monographs (and this is going to be a good thing for the people who write those texts, but more on that later). There’s probably a good place for magazines on eReaders but I’m not quite sure on what that is. Many of the books at the top of best-seller lists will find a lot of their sales (or in the Kindle’s case, rentals) moving very quickly to eReaders once there’s a critical mass – which makes sense for the most disposable (if fun) stories. Nobody’s really that well-served by several dozen more Dan Brown books ending up in used book stores.
In the end, eReaders represent not a replacement for books but an overlapping-but-complimentary form. They’ll absolutely cut into book sales but there will be a new equilibrium whereby booksellers will be able to more clearly see what their market is, and isn’t.