Personally, I think e-books will be practical when these requirements are met:

1. The reader isn't bulky.
2. Random access is easy.

1. I read Safari regularly on my Zaurus SL-5500. It is a hell of a lot less bulky than 500 pages of paper. ;)
2. I like the ability to bookmark multiple pages and then access them like a TOC. I feel having a TOC, topic index, "goto page", and search beats your version of random access.

We use books the way we do because their form makes it convenient to do so. Using an electronic device (assuming the design is tolerable and these features exist) is a question of rehabituating yourself. For some reason, people don't like the unfamiliar. :)

--
Allolex