While I've had some success installing Solaris 11 via KVM on a RHEL 6 platform, Solaris doesn't recognize the default "virtio" hard disk used for KVM. I've had to create a custom virtual IDE hard disk for the Solaris 11 installation.
Is that something that Solaris engineers might address in the future?
Follow-up, Nov 17
I've just tried to set up a dual boot between Scientific Linux 6 and Solaris 11 on a KVM system. SL 6 is on a virtio disk, and Solaris 11 is configured on a IDE disk. When I boot and try to install from the live DVD, the installation stops cold (waited two hours) at 99%. I suspect it's because of the virtio disk.