Readwirteweb once wrote a post about this "the case against reading for entrepreneurs", good read, http://www.readwriteweb.com/start/2010/08/the-case-against-b...
The guy quoted in RWR slammed case study books because they are soft-touch "how to build great companies" - but that's only SOME of them. The - you guessed it - fluffy ones.
"Don't read books that are nothing but fluff" is just not a battle cry people click on, so instead they say "don't read business books!"
Read Positioning, Spin Marketing, Pricing with Confidence, Getting to Yes, Rules for Revolutionaries, Purple Cow, etc., etc.
If you read, say, Purple Cow, or Positioning, or Pricing with Confidence, and don't come away with actionable ideas, you either have an empty head or were just running your eyes over the words and not thinking.
And read lots of biographies. They're practical storytelling - learn from me, kid - pinned down on paper.