This is one of the reasons I love the DS, and Nintendo generally, as they come up with far more interesting and original ideas compared to Sony (barfs on keyboard), and other games manufacturers.
I looked into this back in October when it came out in the states (and I almost brought it. Glad I waited now that it's here), and although there are one hundred books in there, some are multiple entries by one author (i.e four or so Shakespeare's, five or six Dickens' e.t.c), so it's just a case of checking how many of the books you already own (if you have more that fifty percent of the books already it might not be worth it) but I doubt most people do.
But it's still not so bad, considering that it only costs £19.99. (There's a kick in the balls for I. Reader!)
These book cartridges have been available in Japan for years now and are very popular there, it's just a case of waiting to see how well it does over here (looking at how well the brain training and cooking guides have done we may be surprised by just how well it does).
It's because of things like I. Reader that I hope this really takes off over here and they make more. It would cost so much money to buy the same number of books for a digital reader.
And think how much you would spend in a shop, or on Amazon for the same number of books. We're talking a couple of hundred pounds or more!
I'd still go out and buy a copy of any book I really love, but for just reading new things and old classics that I'm not sure if I'll like or not, it's a very good idea.
It's like putting David Tennant in Hamlet, If it gets more people interested in such things when they otherwise might not be, then it can only be a good thing, as there will be a lot of DS owners who will buy it just out of curiosity, and might just end up liking something they read on it.
In response to Veg Chick, there are different brightness settings for the DS screens (which are better now in the DS Lite then they were in the old DS, and the battery lasts longer between charges), and you can adjust the text size to the size you like best. Just goes to show you that a £99 thing can do everything that much more expensive thing can...plus it can play games.
And the DS is so much smaller and more portable than an I. Reader and the cartridges-if you haven't seen them before-are tiny, like an SD card, so ha ha ha again to Sony X-D