This is good advice. I would add:
1. The social media manager should understand your audience and be able to speak in the language of your audience.
2. They must be willing to offer consultation and coaching to get others at the company thinking about how they can contribute to social media (but that could come back to passion, I suppose).
3. Creativity is just as important as passion. Nothing goes viral without it.
I'm a publicist who has grown more and more involved in social media as the tradtional media is, erm, imploding. I wonder how long before the two job descriptions merge entirely.
@Karma Bennett Great tips to add Karma (awesome name by the way). I think it's just a matter of time before the two positions do. As Bob Dylan says, "times they are a changin".