Since Google announced their new free public DNS service, there has been a lot of talk about the speed of various DNS.
If you'd like to find the fastest DNS for your location, use the free Namebench, which tests well-known DNS as well as your regional DNS.
I had been using OpenDNS, but it turns out my ISP's DNS is 53% faster!
[robg adds: The test can take a while to run, and on my machine at least, I wasn't able to use the net while it was running -- lookups kept timing out until the test was over. The end result, though, is quite useful.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091207221026406