Chronosync
One important aspect of tools like the daybook (or like a moleskine notepad, for that matter) is that you want them with you, all the time.
Another is that you want to know you'll never lose them.
That means you need to keep copies in several places, just in case something happens. I'm playing with ChronoSync, a nice little $30 application that makes it easy to synchronize a briefcase folder on my laptop with a corresponding folder on my office desktop. It's not going to displace Retrospect for backup, but it's great for this task.