There are two things to consider: the ebooks availabity, the software, and the hardware part.
The ebook availability is quite good. Majority of non-copyright wokrs (i.e. pre 1934) ara availalbe in places like Project Gutenberg and many others. New stuff (let's forget about pirates, please) is not as common, but there is some progress - I am especially amazed with great (and profitable) experiment of Baen Books, which sells their works though Webscription.net and in addition, offers MANY (as in dozens) free books in their Free Library as an apetizer. Do read this Usenet post when one of Baen's writers elaborates on the idea behind the Library. I just love such optimistic ideology...and when it comes true, it is a cause for celebration. Hip Hip Hurray for Baen, I say :)
The ebook software is quite fine - I presonally prefer the Standard Generalised Markup Language - i.e. your normal html, with added things like it remembers where you closed the window and is very easy to navigate (especially compared to some proprietary things I have seen. Microsoft Reader...horror...imagine your book hanging up...bleh).
It is the hardware that doesn't deliver. PDA's are evolving - and in few years may become as good as normal books (i.e. light and readable), but today? Of course you can read on your normal PC (desktop or laptop) - which I do from time to time, since the alternative (normal book) doesn't exist, I can't easily buy it...or is prohibitvly expensive.
You call THIS a book? Naaaah. Pull the other one.
Try again in 3 years, I say.