Some quick market news for you: SWSoft is planning to release a combined Virtuozzo/Parallels virtualization platform by year-end. According to this article in Computer Business Review, the combo will be available either as a Parallels hardware system with Virtuozzo features, or vice versa.
Ideally, the company will figure out a way to deliver the benefits of each system without the drawbacks. In Virtuozzo's case, that would be the OS-level virtualization capabilities, but not the fact that it needs all apps to use the same OS, all the way down to the patch level. Parallels, meanwhile, offers multiple OSs via its hypervisor, although at the cost of performance overhead and management drawbacks.
SWsoft's goal is to deliver a unified virtualization management system to rival VMware, Microsoft and XenSource. But it's difficult to say how successful it will be. After all, this is the company that only recently admitted to having acquired Parallels -- in 2004.