In my understanding, moderators have a very important role here on SPSE. Note: not dominating, but important. So, what are their responsibilities?
First of all, moderators are the people who keep up the quality. That's an essential point, because quality provides the whole site reputation. And moderators can influence community to care about it. Not by force - mostly by posting comments or reproofs, and also by leading by example.
I'm always trying to do my best in terms of quality: you probably have noticed :) I have now a bunch of article-like answers here on SharePoint SE. These answers are my input, my contribution, my blood and tears.
And cannot resist to mention: it is not the luxury rush! You can check it yourself: comprehensive answers are rarely earn many upvotes. I know this, and consciously, not going to change. Because I like the site, and that is what I can do for it: post qualitative answers.
The other thing which is also very important here on the site - is a positive climate. Community there people are exceedingly jealous, is fragile. Noone wants to upvote answers of their fellow community members, because there is a kind of greediness competition between them. But when one rarely gets upvoted, sooner or later, he will leave...
So, one of the responsibilities of moderators here - is to always upvote decent answers. To keep people on site and to maintain their good mood by respecting their effort :)
Btw, that's why moderators have to be competent (to recognize good answers). The only measure of competence here is the rating points. And I'm now the 11th in the list of top-rated users here - although my first answer is dated Apr 8, 2011 (so I'm only 6 months aboard).
I'm ready to devote myself to SharePoint SE, because I love it, and I want it to become even better. Also I have a deep experience with SharePoint, good rating, I'm active expert here, and also active blogger, opensource contributor and speaker.