CLUSTERS
Also keep in mind that IBM® Lotus® Domino™ fails over to the most available server in the cluster, not the closest server. For example, if you have three servers -- one in Boston, one in New York, and one in Hong Kong -- the Boston server would fail over to the Hong Kong server if it is more available than the New York server. You can control this behavior to some extent by changing the server availability thresholds on the cluster servers.
Using a cluster over a WAN is a good idea for disaster planning. Having emergency backup servers at different locations is a good way to ensure that necessary data is always available when you need it.