Every time someone mentions how awesome new technologies solve live VM mobility across WAN networks, I start muttering unmentionables. Live VM mobility across disjoint layer-2 subnets works great in demos, but usually fails in real life due to stale ARP caches. The only way to solve this problem for good is to implement EC2-like layer-3 forwarding in hypervisor soft switches.
Update: LISP Host Mobility seems to be a potential exception; see the comment from Nico.
For more details, watch the VM Mobility Requirements video (part of Enterasys-sponsored DCI webinar), read the Hot and Cold VM Mobility blog post or watch the recording of NFD4 session with Cisco’s Victor Moreno.