I've been having an odd issue with virt-manager on 12.04. Generally speaking it works flawlessly, however sometimes it appears to lose connection. I've noticed that this will only occur if I 'reopen' it after closing it in the same session.
IE: Use it for a few hours, then close it out. A few hours later I open it up again and I'm missing a connection to QEMU entirely.
Pictures are here: Working: http://imgur.com/aZbXA
Not Working: http://imgur.com/hyqzB
I've seen a few bug reports around that say this type of behaviour was fixed in 9.1, which I'm currently on.
Is anyone else seeing this?