Before this book I'd never done any real web programming. My background is in compilers and trading systems/machine learning( those two are essentially one in the same), all C++ desktop software.
The book got me up and running, better than any of the online rails tutorials, and there are a lot of rails tutorials online.
One thing I really appreciated was that it didn't just build an app, it actually took you through the steps of deploying on Heroku and using git.
A Lot of other books and tutorials seem to assume you want to build an app and run it as localhost for the rest of its life.
The other nice touch was the chapter that teaches a Rails flavoured Ruby. As someone who had used Ruby for scripting, but never for Rails, I thought this was a nice touch.