I still like paper books, because when I'm reading on the couch with one, there are no distractions. A computer offers too many other things to do besides read.
Another thing that you can't yet do on the computer is highlight. I highlight important sections as I read technical books and it improves my comprehension immensely. As an additional benefit, when I come back to the book, I have to spend much less time hunting around for the information I need - the things that I've found valuable in the past are already made prominent.
Kindles have built-in support for highlighting and annotations, although using the buttons to highlight is surely slower than using a physical highlighter. If you're just highlighting important passages and not every other sentence (as some people are wont to do), it shouldn't be a problem.
Highlighting is very easy, even superior on the iPad. I highlight extensively when I'm reading PDFs in the GoodReader app, but unlike a physical book I can export the marked-up PDF back to my PC and easily index, sort, or modify them en masse.
Another thing that you can't yet do on the computer is highlight. I highlight important sections as I read technical books and it improves my comprehension immensely. As an additional benefit, when I come back to the book, I have to spend much less time hunting around for the information I need - the things that I've found valuable in the past are already made prominent.
Try doing that with a Kindle :)