We put OpenVZ on every server. All customer's VPSs are in openvz vpss. We also use VPS for all internal systems. We run each app in it's own vps - this makes migrating services to other servers easy - if an app starts taking too many resources, we simply move machines. Backing up and more importantly, restoring each service is a snap if you just dump the entire VPS. It might take more disk space, but the time savings makes it worth it.

Regards,
Dave