Which is nice, but leaves the question of what kind of virtual infrastructure to buy completely unanswered. Amazon built its system on Xen because it was open-source, relatively inexpensive and Amazon had the expertise in-house to handle code that's wonky even for an infrastructure product.

The cloud computing world is not going to standardize on Xen, though, or ESX or Hyper-V or any other specific product, panel members agreed. Interoperability and vendor independence isn't just part of the cloud-computing ethos, it's one of the technical requirements.

Virtualization—and the hypervisors, operating systems, VM-management software and all the other components of virtual infrastructures from Microsoft and VMware—becomes only one piece of a cloud-computing model, and not that critical a piece.

Virtualization, according to Rosenblum, who is as responsible as any single person can be for the availability of virtualization in a form that's practical for corporate IT, is a logical step on the evolution toward network-based cloud computing model.

Think about that the next time you have a conversation over whether VMware or Microsoft is a better short-term, long-term or any-term virtualization provider, or whether you're getting fleeced by choosing the one you've already chosen.

Virtualization, as much as cloud computing, is inherently a vendor-independent function, no matter how inadequate or purposely inconvenient the interoperability of specific products currently is.

To work right and deliver on its full potential, virtualization vendors have to give customers the freedom to choose the operating systems, management tools and other products that work most effectively for them.

That, typically, doesn't translate into a single-vendor solution, no matter how much either VMware or Microsoft pushes for it.

Not doing so makes the possibility of adding or expanding IT into the cloud more difficult and that, more and more obviously, is the kind of holdup corporate IT managers just will not be able to abide.