Fedora :: KVM Has Become Unstable / What To Do?

Has anyone else experienced problems with KVM in the last few days?
I've been running KVM VMs for the last year. Until sometime in the last few days they've been working fine. I have three F13 systems that I'm running KVM on, an iCore7 with a CentOS5.5 VM, a Core 2 with a CentOS5.5 VM and another Core2 with an XP VM. I haven't seen any problems with the iCore7 system but the two Core2 systems are both exhibiting serious problems.

The CentOS VM is hanging. I can ping it but I can't ssh into it anymore. Prior to that state I was able to ssh in put I couldn't do a ps. Eventually I couldn't ssh in anymore. This is repeatable, I've rebooted the system a couple of times and restarted the VM, it always crashes in the same way.

The XP VM is running but the networking is behaving strangely. Basic networking is working but I can't access the Workgroup although I can access network mounted SAMBA shares that I had previously setup. This could be a SAMBA issue but it started happening at the same time as my other problems.

Another problem that I had was that the virtual disks on multiple VMs on both systems became unbootable. I was able to fix this by removing the disks and then adding them back.