With more and more people moving towards using a global DNS system (like Google DNS and OpenDNS) the speed advantages of a CDN may be cancelled out.
Most of the major CDNs use geotargeting based on where the DNS is being resolved from. For example Facebook's CDN solution (using Akamai) resolves static.ak.fbcdn.net to 210.55.501.200, a 5ms response time. Using Google's public DNS server (8.8.8.8) the same domain resolves to 72.246.43.42, 72.246.43.32, a 200ms response time.
So while using Google's DNS/OpenDNS may save a few ms while resolving a domain, it may slow down a site by putting the CDN pops further away from end users. Until CDN's can work with these public DNS providers the internet may become slower for those using these services.