Books about fast-evolving fields can, obviously, get out of date pretty quickly. One solution: turn it into an iPad app that gets updated as needed.
You know, the funny thing is that I had this thought to myself yesterday while at work. Science textbooks, especially, would be more useful and more ecological if they were electronic and easy to update rather than print all the time.
Man, that could wreck the education publishing industry unless they got their crap together. (I have ideas. Call me.)