I have seen that some IP addresses are tied to multiple servers (physical machines). Example: check the ping times of one of GoDaddy's nameservers:
It has a ping time of around 3.2 ms from Singapore AND a ping time of 2.3 ms from Ashburn, U.S.A, etc. So I am pretty sure it pings the nearest server.
How does one set this up? Is it possible for an average webmaster to set things like this (buy servers in multiple countries and tie them to a single IP address)?