Ask HN: Have your written a technical book?

I am currently in talks with a few publishers who are interested in a book related to a Free and Open Source project I started. The idea of writing a book is interesting to me, but I am uncertain about the terms - it doesn't look very lucrative, but perhaps there is a long-tail from the authority and fame it could bring. People of HN - have you written a book? What was your experience like? What lessons can you share? If you had to do it again, what would you do differently? My biggest question is - why go with a publisher at all? Other than the distribution channels and the vanity of having a printed book with your name on it, it seems like self-publishing could be a much more profitable route. Anyway, I'd love to know anything you have to share! Thanks!, R