To quote wikipedia:
Scrum is facilitated by a ScrumMaster, whose primary job is to remove impediments to the ability of the team to deliver the sprint goal. The ScrumMaster is not the leader of the team (as they are self-organizing) but acts as a buffer between the team and any distracting influences. The ScrumMaster ensures that the Scrum process is used as intended. The ScrumMaster is the enforcer of rules."
Working on this basis, and the fact that most businesses are running 2-3 projects at a time, what actual work tasks does a SM do to fill a full time job? Or, is it not a full time job and that individual do other things such as development, sales etc?
Do any SM's out there have anything to share?
Please note: this question and answer is over twelve years old. The consensus understanding of the role of scrum master has moved on massively since then and so I no longer view this as a valid answer to the question, let alone one worthy of being the accepted answer. By all means downvote it. Beyond that, pay it no heed.
The Scrum Master will do things like ensuring scrums occur, organising sprint planning meetings, retrospectives etc. Also (s)he will be able to explain to management what the team is doing and why the team members cannot be poached off onto other projects until the sprint finishes. Beyond that, there aren't really any defined tasks for the Scrum Master. So one person should easily be able to be Scrum Master for 3 teams, and still have time left over to either do management type jobs (holiday requests, procedures, attending boring meetings with directors or whatever), or be free to contribute to the development resources of the team.