I have been an advocate for open textbooks. I think they are a good way to cut costs and put more textbooks in the hands of our students. But I'll admit that they are not widely used.
There are a number of possible reasons for that. They aren't easy to find, even though there are a number of sites that collect open and free titles. Instructors don't always trust that titles are "as good" as commercial textbooks. It also takes time to review titles for adoption.
The University of Minnesota has started its own online catalog of open books. In an effort to reduce costs for students, the College of Education and Human Development created the catalog to be reviewed by faculty members. The books are all released under a Creative Commons, or similar, license, and instructors can customize the books to fit their course needs.
Students can access free digital versions or purchase low-cost print copies of open textbooks. The university will pay its professors $500 each time they post an evaluation of one of those books, and professors who have already adopted open-source texts will also receive $500. (The money comes from donor funds.)
They hope to address faculty concerns about locating texts and having quality control over titles that have been peer-reviewed. They have almost a hundred books in the catalog.
Although it is encouraging that UM is working to get open textbooks used on campus, I find it discouraging that they need to duplicate the efforts of other repositories that are collecting textbooks and reviews on a larger scale.