Bad screens, bad batteries, l337 W@rez Pir@te5.
As it turns out, computer screens are miserable, hateful things to read on. People read on computers because they have to, not because they want to. Modern "electronic-ink" technology had improved the readability of ebooks somewhat, but other technological challenges remain--most notably, battery life. As an example, our favorite book here in the Cracked offices--the novelization of Batman Begins--never needs its batteries recharged. Can an ebook ever make that claim?
Actually, what exactly is the advantage to carrying an ebook? An MP3 player is great because it prevents us from having to carry a backpack with 100 CDs in it. An ebook isn't any more convenient to carry around than a paperback, and you can use the latter to swat a fly if you need to.
Probably the biggest obstacle, though, is piracy. We all know what happened when MP3s arrived on the scene. Internet pirates began treating the music industry in a delicate manner normally reserved for prison rapes. Wherever publishers are offering content for download, there is someone out on Gnutella offering it for free. As it is for music and movies and software, it will be for books.
Given the hurdles, we can't imagine ebooks taking off any time in the near future, even if they are probably inevitable in the long run (when we run out of trees, if nothing else). What seems most likely is that "ebooks" won't be separate devices at all, just a way to read the books on the next generation of all-in-one devices (a cell phone/MP3 player/PDA/taser). Why people in the future will still choose to read novels when they're constantly bombarded with opportunities to download clips of the popular future television show "Fisting With The Stars" is harder to say.