I believe Tom Peters has for some years now offered up his own set of powerpoint slides gratis; in fact, he regularly uploads the most recent versions of them.

And you yourself David have offered prodigious amounts of content for free over the years.

I'm not sure how to think about what to offer for free and what to charge for.  It's not a moral issue, I'm sure there's more than one answer, and I'm sure part of the answer is "it depends," but-- what does one charge for, and what not?  

Shrewd idea.

That's very cool. It is one of the most commonly used method by internet marketers. It rarely happens in physical books. However, I found one book is doing a good job in a similar way too. You can refer to Roger Hamilton's "Your Life, Your Legacy" book. It used the following strategies:

1. The book talks about creating wealth. And to create wealth effectively, you need to know which is your wealth profile.
2. The book then explain about the uniqueness of each wealth profile and give example of successful people according to those profiles. For example: Bill Gates is a creator wealth profile, Warren Buffett and others are in other profiles.
3. The book then share how to leverage and use the value of each profile to quickly build wealth.

The last part which is the best part is "If you want to know which wealth profile you are, please take a test at our website". The test cost you $100 and the book cost you around $20.

It's a great book and I would like you to read it too.

David, twenty five years ago, you would have had to sell real slides!  

It seems to me like we're moving toward a "give away the content" but "sell the experience and access" economy. Books, by and large, don't make money, but they do function as the front end for other goods and services. The more highly valued goods seem to be contact with the expert and subscriptions of some kind.

There is a point here that powerpoint slides have become the currency of business conversation beyond books or even articles.

I actually approached another noted business writer a few weeks back because I wanted a 20-slide deck of his book to use with internal stakeholders. I would gladly have forked out $10 for it but he gave me something gratis.

I would suggest giving away a slide deck with the book and pricing accordingly. Fans will use the deck to sell the ideas in the book to others (& thus sell more books). The lazy will only read the slides - but there's not much to be done about them in any case.

I like the way in which Newton's equation is used in David Cottrell's book "Leadership Energy", as this presents the most powerful strategy for a successful business.