I recently met with an executive who is planning to pilot a Scrum team at his company. One of the questions that he asked was what where the qualities one should look for in a ScrumMaster. Most of the answers I gave him where consistent with an article Mike Cohn posted regarding this topic (btw, excellent article).
After giving it some thought, I think the one KEY quality of a good ScrumMaster is that they must get "it". What I mean by that is that they must really know the goals of what Scrum is trying to do and and achieve. Agile and Scrum is not about learning a set of rules and processes and then following some cookie cutter method of implementation, rather it is a set of ideas, principals, and goals that are to be achieved. And by achieved, I don't mean just achieved by the team delivering value, but also by the ScrumMaster working with the team and the company in forging a process /atmosphere of empowered optimizing evolving value delivery. To some people, those last five words may seem to be just a bunch of keywords strung together, but I think a ScrumMaster who gets it understands what I just wrote.
At my last client engagement, the ScrumMasters of the company pretty much got it. There were slight difference in implementation details, but everyone was working towards the same goals and optimizing their teams around a company culture and vision into delivery. They weren't following process for process sake or because some book told them to, but they were trying to identify where the values and efficiencies were and how to properly leverage them.
When a ScrumMaster does not get it, you have issues. Many middle managers tend to micro manage or task and order their teams. New ScrumMasters who came up as developers may have a hard time letting go of the tech side and may get too involved or prescriptive in dealing with their tech teams. ScrumMasters with a PMI/PMBOK background may try to implement Scrum with too much rigidity and process. These are signs that these ScrumMasters may not yet fully get it.
For all ScrumMasters out there, that a step back from your Scrum boards (assuming you are using Scrum boards) and think about this: Are your processes really following the heart of what Scrum and Agile should be bringing to you, your teams, and your company?
As a side note, once you get it, your team gets it, and everyone is firing on all cylinders, the job of the ScrumMaster becomes one of the easiest jobs in the world. Good luck getting to that point!