I've used Google's DNS's servers for many years as historically they have been more reliable than my ISP's. In addition when we've made DNS changes on Digiex they have propagated to Google's DNS servers many hours before my ISP's.
OpenDNS has useful features such as been able to block sites, view statistics and so on. People with not so advanced routers have been using it to block Nintendo's update servers for the Wii U.