Domain name system (DNS) might be an alien term to you, so let me give you a brief information about DNS. Domain Name System (DNS) is actually a database system that translates a computer’s fully qualified domain name into an IP address. Computers on a network uses IP addresses (which are not easy to remember for people surfing the web) to locate and connect to each other.
The DNS allows you to connect to another networked computer by using its user-friendly domain name rather than its hard to remember numerical IP address.
The average Internet user performs hundreds of DNS lookups each day, and some complex pages require multiple DNS lookups before they start loading. This is something that slows down your browsing speed.
So in order to make your web browsing faster, secure and reliable Google has launched a new DNS resolver, and that’s Google Public DNS. It’s a free, global Domain Name System (DNS) resolution service, that you can use as an alternative to your current DNS provider.
The need of Google Public DNS?
According to Google speed really matters for web surfers and if same holds for you then you should give it a try. Here are some advantages of using Google public DNS.
1] Google public DNS reduces DNS security threats, thereby giving you a secure web browsing experience.
2] It makes your web browsing faster.
3] It brings you the results without any redirection.
If you are willing to try Google Public DNS then head over to Google Code Blog for detailed instructions on how to set up Google Public DNS on your computer or router.
Shahab khan is a Tech blogger from India & a founder of VirginTech. He blogs about Technology, internet, Social media, computer tips & tricks and Web 2.0. 
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Hope they are better than OpenDns. OpenDns didnt work for me many a times.
Its a pretty nice alternative to OpenDns, go for it. I hope you wold like it!