Looking for geo-directional DNS service

[Hank Nussbacher <hank () efes iucc ac il>]

I am looking for a commercial DNS service that provides 
geo-directionality.  Suppose I have 4 data centers scattered thruout the 
world and want users to hit the closest data center based on proximity 
checks (pings, TTLs, latency, load, etc.).  I know one can "roll their 
own", using various geo-locational data from companies like Maxmind.  I am 
*not* interested in that.  I am *not* interested in applicances like the 
Cisco ACE GSS 4400 either (that do this as well):
http://www.cisco.com/en/US/products/hw/contnetw/ps4162/

What I am looking for is a commercial DNS service.

Is the Akamai Edgescape service the closest to what I want:
http://www.akamai.com/html/technology/products/edgescape.html
Is anyone using it?  Can you recommend it?

Another service I know about is the Ultradns (now Neustar) Directional DNS:
http://www.neustarultraservices.biz/solutions/directionaldns.html
But this service is based on statically defined IP responses at each of 
their 14 sites so there is no proximity checking done.

Thanks,
Hank