My own experience has been pretty different. I took time off of my work to run a business. we even wrote a book  - Now, uh, I needed to run that business, on an emotional level, I mean. but it was a hugely bad idea financially.
When you show up to an interview after spending years running your own company? I mean, I'm sure it's different if you are management, but as an IC? Even though I had written a book it was like I was unemployed for that time. There's no way my wages are anywhere near they would have been had I spent more of that time working for other people.
I mean, my own case would have come out differently if I was able to sell my company to someone big, which may have come down to a few obvious unforced errors of mine?
I mean, sure, sometimes it's still worth it to take time off of work to do something else... but don't say it's not a career hit. It is a huge career hit and you need to include that in the equation.
(When doing the "is it worth it" math on writing books, consider the shelf-life; that shelf life doesn't just apply to sales, it also applies to the reputation boost. My own recommendation to my younger self would have been to get a job while the buzz for the book was at it's height.)
On twitter: http://twitter.com/prgmrcom
Edit: He also has a book: http://www.amazon.com/Book-Xen-Practical-System-Administrato...
Fresh book recommendations delivered straight to your inbox every Thursday.