I am just posting this as FYI as I found it very interesting.
Despite having worked for a university for 18 years and as Program Director and on the academic side for 8 of those years, there are some parts of the university/academic career world that I do not fully understand.
The link below is to an interesting article in the Chronicle of Higher Education. It is on the dynamic of what academics do for free and what they get paid to do, especially in terms of publishing. I found it interesting because I have spent many, many, many hours reviewing articles, theses, dissertations and writing articles and chapters for free. I have done this when I was working for a University and have continued the last 3 1/2 years without an academic appointment. Although the experience of being paid to write has become more common I still don't think it is necessarily routine in our profession let alone being paid to review work.
I remember the first time I was offered a fee to write a chapter for a book that was substantial (more than $200) and was shocked. I had written several chapters before for free and did so both because I was honored and flattered to be asked and because I knew it would help me along the clinical promotion track. I also have dealt with it from the author side. I have authored 2 text books and only with the most recent edition of one did I consider paying authors for their contributions. In the past I considered the free copy of the book, the name on the publication and my heart felt thanks as appropriate as that is what I typically have expected to receive when I have contributed to the text books of others.
I continue to review articles for several journals for free and to write chapters whether there is a fee associated or not. My time has become more and more important to me and making the investment in a well written chapter is not worth a few hundred dollars if it the opportunity costs are not worth it. Many times I would say yes even if I had to pay to write! LOL.
In the OT world writing text books is certainly not going to help you be "set for life." If you have an extraordinarily popular text it is a nice supplemental income that can help with one of those ski vacations that take with joy and without an ounce of guilt! LOL While my management text has done relatively well I still joke that on an hour for hour basis I would do better to invest the time as a barista or bartender than I have on writing.
If you have interest, please check this out. BTW, I found the link from Matt Zwolinski's Facebook page. He is one of the lead contributors to "Bleeding Heart Libertarians" which can be found at http://bleedingheartlibertarians.com with the tag line of free markets and social justice.