And if you're going to configure your own DNS/Nameserver network. Make sure the servers are diversified correctly & in/or near major internet backbones.
I.E.
Chicago, Los Angeles, Miami (example: Mojohost), DC region + Ashburn/Reston VA, New York City (example: Webair), Atlanta (example NationalNet) & Dallas, TX.
And if you're making real money from euro/asian/south pacific traffic.
Euro-zone UK, Netherlands 'Amsterdam of course' ( example: webair), Sweden (excellent infrastructure); Latvia, Czech Republic & even Romania.
Asia: South Korea, Japan & Hong Kong (They all have outstanding infrastructure to cover most of the Asia-pacific region) So choose the best 1-3 to suit your traffic needs.
Australia: you've got New South Wales, Victoria & Melbourne if that's a main market for you. However I don't know too many people expanding their name-server distribution into Australia yet. I would imagine something like UltraDNS might have an AU a presence.
South America: Although a typically Miami is used by most networks, you may want a presence in an actual South American country with real infrastructure in order to drop an extra few milliseconds. I would only suggest Brazil, Panama, Argentina....
Also if you're not happy with your LA presence (for S.American purposes), you can get a decent connection Mexico these days, which would make you one step closer to S. America without having an actual presence in the deep southern regions. However I've always experienced extreme latency issue's in MX. Mostly time-of-day "rush" dependent but not always.
Hope this shed some light for a few people
I'm out!