Peter Lacey Williams posts here and here on how to version RESTful Web Services using custom MIME media types and I find this very interesting. I do find the following quote about the browser a little curious:
They (browsers) are almost certainly not the target consumer of the services
If your web applications are RESTful in nature, then the browser is definitely the target consumer of them. So I’m not sure if Peter is suggesting that with services that return HTML as a content type, there aren’t versioning issues or that services that would face versioning issues generally do not use HTML as a content type.