Comment 17 for bug 187048

You do not need to be a member of those two groups.

You need membership of libvirtd to manage the system-wide libvirtd instance (qemu:///system), and you need membership of kvm to run virtual machines as yourself (qemu:///session). If you're using virt-manager for other purposes, you don't even need to be a member of either.

For intrepid, I'll make sure the error messages are more helpful. I will not, however, be automatically adding users to any of these groups.