It was used for a US presidential election debate in 2008 and 2012. But other than influencing the course of human history it has enjoyed little traction.

It was launched in September 2008 - http://en.wikipedia.org/wiki/Google_Moderator

The one person I saw using it, at least when it was relatively new, was Matt Cutts to organize the questions asked for the daily Google Webmasters videos. Though those seemed to have died out almost a year ago, and they had moved to the Product Forums by then anyway.

Same here.

Just wanted to chime in before everyone starts talking about how google never sticks with their products, this is relatively unknown and better alternatives exist. There is no reason to keep this service up.