KVM on a Cluster?

[Mat]

Hello,

The cluster stack found in the wiki[1] looks very promising and I'm 
looking forward to testing it out. One thing I've been thinking about 
lately and looking for online is the possibility of running a virtual 
machine with KVM on top of a cluster.

Is it possible, or even practical to run an application like KVM on a 
cluster? The reason driving me to think about this would be hardware 
redundancy, and the ability to make "live" backups of a virtual machine 
by isolating it from the others (a script that temporarily disables the 
network?) and shutting it down for a snapshot.

Unfortunately, I have very little practical knowledge and experience 
when it comes to clusters, so please feel free to enlighten me if I'm 
proposing something crazy.

[1] https://wiki.ubuntu.com/ClusterStack/LucidTesting

Thanks.
matoc