In the never ending quest to give the user the fastest initial page load response, we came across GeoScaling's location based DNS service. Last year we had searched for such functionality but the available offerings were prohibitively expensive. When our servers cost as low as 10 dollars a month for a virtual slice of a Unix server, there is no way 400 a month fits into the budget for DNS services. That being said, we did not look at GeoScaling because they have a free offering, it was strictly for their advertised location based IP resolution. Initially I was a bit skeptical, but without too much fiddling I now have a "phpish" script that does serve the IP of the closest server, fails over if it is down, and accepts our call into their servers to take a location / server "offline" if we are about to do a software upgrade. We monitor 4 different servers (CA,TX,GA,IL) from 3 US locations (monitis) for initial page load time. After tweak out all we could with compression, delayed JS loading, "optimizing" our flex application bootstrap swf (all of our app is in flex modules so only the module in use is loaded on demand), it became painfully obvious that the remaining nut to crack was latency caused by the distance to each datacenter. I have the numbers / stats to prove it, but expect a 2 to 5 x gain with geo based DNS (assuming at least 3 regional servers). Put another way, our goal is to have the initial page load take 1 second (before anything is cached in the browser), and we found that going to the wrong (farthest) server sent those times up to 5 seconds or beyond when we were achieving a second or less testing from Clearwater Florida to our Dallas or Atlanta servers.
I offered to write this testimonial considering I believe what GeoScaling offers to be unique. I have been using Dnsmadeeasy for many years, and have never had a problem. They are just now going to beta their geo based solution, but I doubt it will offer the flexibility of be able to have the resolution be tailored to exactly what you want via the php script and client uploaded data. Also be aware a large portion of the geo DNS offerings are country based, some are region based, but very few offer true lat/long distance based resolution.
If you have questions about our exact setup or results, or how we achieved it, I can be reached at firstname.lastname@example.org