Luckily, we've had very few problems on here...but some other forums that I frequent aren't nearly as lucky.
The main purpose my set of moderators perform here is to remove pornographic material and other offensive material (which we have had to do a few times), edit or remove posts from people that may have accidentally double-posted or had a problem with their original post, and just generally be a resource available to help new members.
I'm hoping we continue to be as lucky as we have been so far with having such a great group of members! There are a lot of people (usually "kids") that roam the net with plenty of time to jump in to places like these and post spam, offensive material, or just generally try to stir up trouble. We had one person like that a few months back and, thanks to my mods, it was dealt with quickly and I would doubt anyone here ever even noticed.
So, to wrap up a long post, I see your statement as a great compliment to all of my moderators. They do quite a bit in the background...and they do it so well that most people will probably never even notice the things they do that help make this a great place.