When does a blog become a book?
When the subject is compelling, has a wide appeal or answers the particular needs of a potent niche market, and is well written.
Here's an example. Writer and editor Chris Anderson (The Long Tail) started working out his ideas about this economic model on his blog, The Long Tail. As he posted ideas and information about this new way of understanding the impact of the internet on our economic realities, he drew comments from his readers which strengthened his arguments by making them sharper. Readers also added their own experience and observations and suggested avenues for research until Anderson had a fully vetted book that turns our conventional understanding of the manufacturing, marketing and selling of merchandise on its head.
Check out Anderson's blog, The Long Tail, and seek out a copy of his book by the same name. It a whole different way of looking at yourself as an entrepreneurial author.