It seems to be targeted primarily at EC2 users, but I would assume this works just as well if you have your own servers in multiple regions, right? Like the (more expensive) Global Traffic Director of DNS Made Easy.
Yes, this works for non-AWS servers as well, as long as they are reasonably close to one of the available AWS regions (currently Virginia, California, Oregon, Ireland, Japan, Singapore, Brazil). For example, if you have servers in Texas and London you can tag them with regions us-west-1 and eu-west-1 respectively.
End-users will be routed based on measurements from the AWS data centers in California and Ireland, but this will only lead to incorrect results for a small percentage of users for whom the difference was small anyway.