If you watch a lot of netflix, hulu, and such, switching your DNS from your ISP's DNS servers isn't always best. CDN's use dns servers to find your geographic location. OpenDNS, Google DNS, and other's make it look like you are geographically located elsewhere. This can cause slowdowns. I had this problem a couple years ago with netflix when I switched to OpenDNS. Once I switched back to my ISP's (time-warner) DNS, the issues went away.
At it’s simplest, the DNS server does a geographic lookup based on the DNS resolver’s IP address and then returns an IP address for an edge server that is physically closest to that area.
http://www.nczonline.net/blog/2011/11/29/how-content-delivery-networks-cdns-work/