Interesting discussion in the Scrum Development Yahoo group called Scrum Master and Project Manager roles. These posts go around the question:

Should [the roles of ScrumMaster and Project Manager] be fulfilled by the same person or by different people?

Great answer here by Ken Schwaber, the father of Scrum, about the paradigm shift of management in agile teams:

just” shift from predictive, “I can make it happen” thinking to empirical “what can I do to help things get done and transparent” thinking

Easy to say, hard to do (achieving good results). My opinion is that it worth it !!