Eoin Purcell
Making Money Twice
Read this. The key quote:
That’s roughly $765,000 over a few years off roughly the same content. Insight and ideas about how we run our business. Blog entries, PDF, paperback, and conferences.
But all of it is worthwhile and important!
I’ve been more awake!
Eoin
Eoin Purcell's Blog 
“We probably could have done a few more things and pushed that total over a million.”
That’s an incredible amount to come up with using the same content/idea and just discussing and repackaging it.
It really is.
These guys have impressed me hugely for a log time.
Their approach is refreshing. the charging for a pdf because they believe it is worth something is a real kick in the face tot hose who believe that you cannot charge for digital content.
Equally though it shows how the key is new and exclusive content rather than general/common content!
Eoin
PS: I used their backpack product for a long time until I found a desktop replacement that suit me better.