Postgresql on high availability websites?

I was looking at the pingdom infrastructure matrix (http://royal.pingdom.com/royalfiles/0702_infrastructure_matrix.pdf) and I saw that no sites are using Postgresql, and then I searched through highscalability.com and saw very few mentions of postgresql. Are there any examples of high-traffic sites that use postgresql? Does anyone have any experience with it? I'm having trouble finding good, recent studies of postgres (and postgres compared w/ mysql) online.