Spoiler alert: you can't really get anything signifant+useful done with that book, because Haskell is a language where only experts can get anything significant done.
I have to strongly disagree on that point. I'm certainly not an expert (I hadn't done any meaningful programming in 10 years prior to reading it), and I found Real World Haskell immensely helpful in building a production system that receives and processes security events.
In fact, the chapter on building a Syslog server was incredibly useful, as the first piece of the system I'm building processes events which look a lot like Syslog (with some JSON embedded in the messages).
I will say that I had a hard time getting through the book as my only Haskell book. I ended up using Hutton's "Programming in Haskell" as a supplemental resource (selected mostly because it's a very small book).
Spoiler alert: you can't really get anything signifant+useful done with that book, because Haskell is a language where only experts can get anything significant done.
If you just want the mindblow experience of Haskell: http://conway.rutgers.edu/~ccshan/wiki/blog/posts/WordNumber...