I've never had a scrum master across 7-8 companies. Usually it was a rotating role, or a manager/tech lead. But certainly not one person dedicated to it.
spotify seems to have a few professional scrum masters and it seems to work for them. I'm less interested in typical cynicism and more interested in how this gets done -well-. Any spotifier's care to comment on having fulltime scrum masters?
edit: It seems they are called "Agile Coach"es.. is that any different?
Unfortunately I've seen people with it as a job title. They were the absolute joke you'd expect.