Presentation by Qualcomm on their experience migrating from Xen/RHEL5 to KVM/RHEV6.
Straightforward advice — plan, plan, plan, then do.
Qualcomm reduced hardware deployment significantly and simplified management with the RHEV tool suite — significant operational savings.
Qualcomm made extensive use of the virt-v2v tool, but had to modify it (yay Open Source!) to make it cluster (RHCS) aware. Modifications are shipping with RHEV 6.3.