I've been trying chess ebooks lately. There are some real advantages for me, but whether those apply to you depends on your learning style. With a book there have been many times where I skip some examples because the lines go too long for me to properly visualize - so yes I need to set up a board. Many variations introduced to an example mean I have to constantly re-set the position and play through.
Now that can be an advantage - perhaps the lessons sink in more because of the time being taken, but with limited time to spend on chess - and a certain amount of laziness - I looked into ebooks.
There are a couple great apps now for iPad, eplus books and also gambit. What I like about these is you tap on an example and the board is immediately set up. Move forward through the moves and they are replicated on the board. You can easily re-set the positions by tapping at the start again - or try your own variations by entering your own moves. Flip the board, change board size etc etc.
This results in me getting through more examples and understanding them better because I can easily repeat sequences many times.
I've run out of shelf space in my library so ebooks are another advantage there, and if I've got my iPad with me on the train there are several books I can use, without the space and weight of carry chess tomes everywhere.
Some ebooks (e.g. Silman's Endgame Course) have audio snippets included. I don't think they're completely necessary but it does increase my enjoyment of the ebook. I believe in the future there may also be videos embedded in some ebooks.
Then there's the "I want it now factor". The books download pretty quick. Unfortunately there isn't a huge range to choose from yet but that will change over time.
The (free) eplus books app comes with Capablanca's Chess Fundamentals, so you will be able to see whether you like using an ebook or not, before spending money.
So far I think I prefer the ebooks, but I still enjoy my "real" books. In the end it comes down to whether you remember things better by setting up and handling real chess pieces, or if a 2d board image is enough to get the message through.
What do you think is the best way for learning from chess books? With an ebook (not a PDF) on your ipad etc. or with the real book right in front of you with a chess board?