I bought the Kindle edition of this book having done functional programming with other languages before (Lisp and Scala). The first third or so of this book was material very familiar to me from those other languages and even here I found the book hard work. There were mistakes where the description in the text did not match the sample code. There was an instance of sample code not compiling, and infact the compile error was printed into the book in place of where the program output was expected (maybe this is only present in the Kindle print). Sample code was often too abstract using identifier names that did not help me to understand what the sample code was trying to achieve (ironic for "real world" haskell). In other cases the sample code required functions that would only be implemented much later in the book (very confusing if you are trying out the samples as you read).
The next third or so of the book was new territory for me, and here I found myself often second guessing the text of the book. I suspected mistakes but did not have the confidence to know for sure. At this point the online version of the book proved to be very helpful ([...]). Here there are plenty of online comments from readers of the book that correct many of the mistakes and clear up confusion. Take a skim at some of the comments there before you buy to get an indication of the types of problems this book has.
I gave up on this book at roughly the two thirds mark, and am now instead reading "Programming in Haskell
". I have yet to complete this alternative book but so far it is of much higher standard than Real World Haskell.