The situation in ebook readers today reminds me of the situation in portable digital music players in April 2003, the month Apple introduced the iTunes Store. There were literally thousands of portable digital music players out there, the vast majority of which looked like portable USB keyfobs as far as operating systems were concerned, all of which played open unencrypted mp3 files. Then there was Apple selling their own proprietary-DRM'ed music files -- but it was integrated with the computer hardware and with their iPod music players. In the end people decided the convenience of having one application handle all their content whether local or located on a portable device was more important than the DRM, and the iPod won the portable digital music player contest by a landslide.
Right now, there are only three players that integrate content, software, and hardware: Sony, Amazon, and Barnes & Noble. Amazon's Kindle wins the content war by a landslide, but their hardware looks dated and obsolete compared to the new readers from Sony and B&N. Sony's content situation is horrible -- books from Sony's ebook store actually cost more than paper books purchased in bookstores! The Nook right now is unobtainium and a bit unstable, as you'd expect from version 1.0 of a product, but is decidedly better hardware.
The wildcard is Apple. Will they do for ebooks what they did for digital music? The problem is that the iPad will have, realistically, a 5 hour battery life in normal usage, and that just isn't enough for most situations where I might haul my e-book reader. If I'm doing an intercontinental flight that is 10 hours long, a 5 hour battery life is a "don't even bother" for me. My Sony e-reader, on the other hand, will happily let me read books for 10 hours at a time, and still have plenty of battery life left, thanks to the e-ink display. It's just that my selection of content is rather limited -- all I have on it, for the most part, is Baen Webscriptions stuff (no DRM, reasonable prices), and you can only read so much sci-fi warporn before you're sick and tired of sci-fi warporn.
So I'm keeping my eye on Apple. But unless Steve Jobs has a change of heart on e-ink (which he sneers at) or there's some revolution in LCD technology that allows it to generate readable displays without a backlight and thus get decent battery life (don't care if it's as good as e-ink battery life, but it has to be at least competitive with the Nook's battery life!), the hardware simply isn't good enough. Otherwise I'd be reading books on my iPhone via Stanza or etc., which I'm not doing because realistically I only get three hours of battery life that way -- far less than if I fire up my e-ink based reader.
Oh, what about all these *other* ebook readers? Some of them have nice hardware and software. But it's all about content, in the end. I suspect they'll end up just like all those portable digital music players that plugged in like keyfobs -- they'll still sell, but the readers that allow a fully integrated content cycle (purchase, transfer, read) will be the ones that most people buy, because for most people, they just want to purchase books in a convenient manner and not worry about how they get onto the ebook reader.