Since Asaf keeps badgering me, I'll say a few words.
Despite having the yearling badge, I only really started participating around mid-October of 2010. And that was because my first few looks at the end of summer last year of the site wasn't really favourable, and some of the comment exchanges between users were out-right mean. When I came back more than a month later, some of the rough spots were ironed out, some were still there (some still are); but despite my initial fears Math.SE did not turn out to be another Yahoo! Answers. And that gave me confidence in the community who will form the backbone of this forum. There is quite a variety of problems posted on this website, and answers given tend to be informed and reasonable. And I feel now that having stuck with the site was the correct decision.
Running for moderator was more of a whim than anything else. When I tossed my hat into the ring I was more trying to stir up "trouble" than anything else: I cannot bear to see an election for three seats held with only three nominees! (And I soon see I probably wasn't the only one.) Actually ending up as a moderator is something of a happy accident, and I am grateful to the community for giving me the chance.
I will not say too much about the general user experience, since everyone has their own, and many are surely more passionate than I about it. Overall, what I like most about this site is the community. The Maths.SE and TeX.SE are the two among the SE communities which I am most comfortable with, and that is what draws me back to the sites and that is also reflected in my rep distribution on the SE sites that I participate.
Anyway, let me say something about the Moderator experience.
Moderating Maths.SE has been both easier and harder than I expected. The easier part largely because of the good infrastructure and software design by the SE team. (There are, of course, many things that could be even more awesome in my opinion; but as a general platform that is adaptable to so many communities, I think that the work put into the sites and the responsiveness of the SE team are generally laudable.) I must, of course, given kudos to all the users who regularly use those infracture and tools by participating in Meta, voting for closure/reopening, flagging items for moderator attention, and welcoming new users; their efforts were invaluable in guiding this site to its current form.
The harder part, on the other hand, comes from the community itself. For starters, mathematicians tend to be stubborn creatures, something that, along with small idiosyncrasies, seems to be even encouraged by the culture of the profession. To put it another way: mathematicians make lousy politicians. It is perhaps not surprising that from a profession that has a pretty-much absolute standard of objective truth would be born individuals who would also refuse to compromise on subjective opinions. Mind you that these I have observed long before starting as a moderator here; I just didn't expect the extent to which one may encounter them as a moderator. To complicate matters is the fact that Maths.SE is not just for mathematicians. With the pseudonymous participation (and not all mathematicians wear a T-shirt with the big letter M on it), differing standards (and the split between mathematicians and non-mathematicians is just one such divide; there are many more) lead unavoidably to friction between the cultures without any one individual being the "trouble maker". With a few regrettable exceptions, the cohesiveness of the community allowed us to work through, and learn from, such incidents. And I think the community is growing nicely.