r3dbaron: The order of the nameservers does not have anything to do with the order they are queried in - most nameservers trying to resolve one of your domains will just pick one nameserver at random - at least that would be the expected behaviour.
So if you are trying to achieve a 50/50 traffic split between two parking programs, I would not recommend this method, since it's not going to split the traffic exactly at 50%. It will always depend on where the user is coming from and what their upstream DNS might have cached.
If your parking providers allow you to use URL forwarding, you can use a service such as
DomainManager.com to split traffic between two destinations.
Another reason to be careful which DNS to list is that some parking providers might also check the zonefiles or try to resolve your names in order to see if your name is actually pointing to them.
RazorNF is right though that the nameservers ideally should be located in different subnet - it is surprising how few people stick to that rule. The question here might be what
Luke's goal is - additional redundancy or to rotate between programs.
Hope this helps,
/Frank
