On the community forums a question was asked around Campus Clusters and pinning VMs to a specific set of hosts. In vSphere 4.0 that’s currently not possible unfortunately and it definitely is a feature that many customers would want to use.
Banjot Chanana revealed during VMworld that it was an upcoming feature but did not go into much details. However on the community forums, thanks @lamw for point this out, Elisha just revealed the following:
Controls will be available in the upcoming vSphere 4.1 release to enable this behavior. You’ll be able to set “soft” (ie. preferential) or “hard” (ie. strict) rules associating a set of vms with a set of hosts. HA will respect the hard rules and only failover vms to the appropriate hosts.
Basically DRS Host Affinity rules which VMware HA adheres to. Can’t wait for the upcoming vSphere version to be released and to figure out how all these nice “little” enhancements change our designs.