VMware have just published a new article on their Networking blog around the subject of using VMotion between DataCenters - it's something that has been on the wish-list of VMware administrators for as long as I've been "doing" VMware:
It's currently a "proof of concept" between VMware and Cisco, and some of the details are sketchy at best, hopefully they will either release more information on the link speed/quality/latency between the 2 locations, or perhaps this will turn into a fully-supported configuration.
I've delivered a series of VMware VI3 Fast Track courses to a variety of Cisco techies over the last year or so, and VMotion not being supported across sites, even though technically it is possible, has been a discussion I've had with Cisco techies many times.
VMotion itself is an amazing piece of technology, even within a single location, the concept of relocating an entire workload across onto another x86 system allows administrators so much more flexibility. Taking that same technology out of the datacentre opens up masses of other possibilities in the longer term.
It might not be too far into the future that organisations really start using both their internal IT and external IT as a single entity, all regardless of geographical boundaries - maybe "The Cloud" will happen, and in the way that organisations want it to, after all.
UPDATE: VMware have now announced official support for VMotion up to a maximum distance of 200 kilometres: http://erikzandboer.wordpress.com/2009/09/03/long-distance-vmotion-a-fact/