vMotion, moving a running virtual machine from one host to another without a disruption, is nowadays limited to host located in the same LAN.
VMware is working in long distance vMotion. At VMworld 2009 VMware, Cisco and EMC presented a the results of a joint testin of vMotion over long distancess. This could be usefull for disaster recovery but also for moving virtual machines in and out of your datacenter to datacenters of service providers (cloud). The distance between datacenters is limited to 200 kilometers because of latency requirements.
VMware.com has information on the proof of concept
Eric Zandboer reports on long distance vMotion
For an overview of the presentation see the posting on VirtualGeek
Joep Piscaer of VirtualLifesytle has another report on the same session (TA3105)
An a third report on what was presented at TA3105 is published at TechTalk