David Pogue explains DNS and why OpenDNS is a great service in this video.
OpenDNS is generally fast, has extra features like anti-phishing, shortcuts, and parental controls, and is run by non-evil people (perhaps unlike your ISP).
But you should also check to see what DNS provider gives your particular location the fastest DNS response as we explained in the post Make your Internet faster by changing DNS.
We explained that you can use namebench to test a variety of DNS providers. I recommend running namebench multiple times since results will vary between tests. For me, Verizon’s DNS service actually provided the fastest and most consistent DNS speeds so I’m sticking with them for now for the quickest web browsing experience.
One way to see who is running the DNS on a particular network is to type in a long web address that doesn’t exist. Most DNS providers “hijack” the 404 Not Found response and give you something like the response below from Verizon. It’s annoying that this is a standard practice now, but your ISP and other DNS providers get extra income from search engines for directing people there.