I co-wrote a book ('Web-Graphics for Non Designers') and later tracked it down in a Borders/similar store in London and got my photo taken with it there. Certainly a novel experience for anyone who's not a f/t author, but not so exciting that I'd be dreaming about it! I was writing to a very difficult deadline, fried my brain in the process and it was hardly lucrative.

From my experience, I'd be hard-pressed to be convinced to do it again. I got a few thousand as an advance for writing three of the books ten chapters and it involved research, a plan, fleshing out the content, providing supplementary assets and then a couple of rounds of editing. I've done better out of non-spammy MFA sites in terms of return on time invested.