I hereby nominate myself.

I have been a MO user for over three years now and have been pretty active both on the main site and (less) on the old meta. In this time I have learned an enormous amount of math from MO and its users —most of which I would not have had probably even come across without MO— and have managed to help a few people myself along the way.

I very much think MO is an extremely valuable resource, and I somewhat marvel both at how well is has worked in the past and at how well this success has continued into the present: almost four years of existence, in Internet terms, is an eon. This is in no small part due to the way problems —which have of course arisen— have been managed, and that we owe to both the excellent people which have been doing the moderation and the remarkable set of users the site has.

For some two years now, I have been moderator at math.stackexchange.com, so I am quite familiar with how the moderation tools work at SE: that always helps.