Reactive programming is clearly a trend these days, a lot of front-end developers are starting to take it into account because the nature of their work (event-based, javascript) lends well to it. A lot is being written about it on the web for that environment but, sadly, the back-end is not getting the same amount of attention.
Thanks to Node.js, we now have a very similar environment on the server side that can allow developers to think in terms of RP (or even Functional Reactive Programming) in the same manner that front-end developers think when using that technique on their day-to-day.
This book will be interesting to Node.js developers (or even other back-end developer) because it will provide them with a new and different way to solve the problems they have every day.