Will R has once again articulated something that I have felt for a long time: that textbooks are not the best tool for the classroom.
As an ESL instructor, I have yet to find a textbook that really does what I want to do the way I want to do it. I always end up at least supplementing texts. I prefer to replace them when I can with materials from many sources, includiing the Internet. (Since I wrote the curriculum and decide what books are ordered, I have a lot of leeway here!)
One place we have always used textbooks in our program, though, is in speaking and listening. I know... That seems like the one class where a textbook would be totally unnecessary! But since I don't usually teach those classes, I was reluctant to force other people to create the course themselves. Some of the instructors we have had couldn't have done that if their life depended on it. But this coming year we are eliminating the text in our beginning level speaking/listening class. The instructor, who comes to ESL with a background in corporate training, is more than happy to develop the course she wants to teach. I think it is going to be a lot better for the students.
Anyway, I encourage you to read Will's post if you haven't.