Some time ago, I wrote a number of book reviews for the O'Reilly reviewer program. The basic idea was that they would give out free ebooks in exchange for reviews. They've since discontinued the program, but I thought I'd keep the reviews around in case they're useful.
I generally like O'Reilly books, and I don't mind reading ebooks, but I did find that for certain kinds of topics, not being able to quickly flip through pages makes it harder to use a book as a reference. I mean, yes, there are search functions, but if you don't know the exact term to search for that doesn't help you all that much, and navigation is a little cumbersome, anyway. So, for computing related references, or textbooks, the ebook isn't my favorite format. Unfortunately, many of the books in the O'Reilly catalog fall into this category.
An additional problem is that some aspects of technology (I'm thinking in particular of specific libraries) change so quickly that having something like a book is less helpful than the online documentation. If the API has changed significantly since the book was published, it can actually be harmful, rather than helpful. As it turns out, I haven't gone back to any of these books in a significant way, either to reread them or to use them as a reference, which is unfortunate.
I guess it's a good thing that I paid for them with reviews, instead of with cash.