The thing that scares me the most about relying on a computer is that I have had my computer erase its entire hardrive during finals week. That being said, if I ever did shift to working largely on a computer, I would back up files like mad.
Overall, the directors that I have worked with didn't particulary care for laptops at all--and made it known. So when the situation arises when I want something on the computer, I just take time outside of rehearsal to do it. As it has been said, working with a new script sometimes is easier on a computer--I worked on a show this past fall which the playwright was in, so the script changed nearly daily.
Personally, I trust my handy-dandy (paper) notebook