Rotating Scrummasters - A good practice?

In many Scrum teams a practice has emerged to have the Scrummaster role played by a different team member each sprint. The ideas behind this are many and varied:

1. Rotating the Scrummaster allows more people to learn Scrum in-depth
2. Each team member adds new ideas to how to run the Scrum project
3. Builds skill redundancy for the team. If the Scrummaster gets sick, or quits someone can take over without too much lost velocity
4. Helps empower the team, everyone gets to participate at all levels
   
5. Helps prevent people just reporting status to the Scrummaster
6. etc

But is this really a good idea?

Most of these benefits can be achieved with other means, and some are caused by the Scrummaster doing a poor job at leading the team. For example with number two, that can be accomplished by having a really great and open team atmosphere, or even good, dynamic introspections. You don't need to be "in charge" to bring forward ideas.

Depending on the context I think it could beneficial to rotate the Scrummaster role around. However, not every single Sprint. It makes more sense to allow at least three Sprints to elapse prior to rotating out the Scrummaster. It will take at least three Sprints for that person to get comfortable in their role and get their mind into the Scrummaster space.

Don't force every single person on the team to take on the Scrummaster role! Not every single person has the personality to do the job well and there is no point in setting someone up for failure.

Even if you don't rotate the Scrummaster role around, it is very important for that Scrummaster to train his replacement. People should always be able training one of their peers to do their job. In the military this is institutionalized for very good reasons, but many companies don't factor in the "bus factor" in their contingency plans. This can seriously harm a company or a release cycle.

What do you think? Should the Scrummaster role be rotated? If so what best practices do you have? Or should the Scrummaster role be assumed by one person so that they can master it?