So what is that payoff? Why is client virtualization a big deal?

Number one, depending on how it's implemented, client virtualization can operate on lower spec hardware at the end user location, which offers hardware savings for new machines as well as the opportunity to stretch out the useful lives of already-existing client machines. So right off the bat, there's some capital expenditure avoidance possible with client virtualization. While the savings on each machine may not be huge, when applied over hundreds or thousands of end users, the money can add up fast. Naturally, some of those savings must be applied to the additional hardware necessary in the data center, but net-net client virtualization should offer savings in this arena.

Number two, remember what I said about some—but not all—of the cost savings from less client-side work being transferred to additional work in the data center? It's true that some of the savings are spent, but the rest of the avoided IT operations costs aren't spent. It's hard to estimate what that percentage will be, but considering the amount of money spent on help desks, personal visits on-site to deal with software problems, and so on, it could come to a pretty penny, indeed.

Finally, and perhaps most important, there is the money saved through end users who are no longer stuck sitting doing nothing when their PC gets hosed. Every time someone has to stop working because their machine breaks represents lost productivity. This lost labor cost far outweighs the cost of hardware and software devoted to employees, so using client virtualization to keep client machines up and running can provide enormous financial returns.

Given the financial benefits client virtualization offers, why doesn't everyone take advantage of it at once? As I mentioned earlier, server consolidation has taken off because it offers a sustaining innovation: it can be applied with very little change in behavior or processes. By contrast, realizing the benefits of client virtualization requires significant change in those areas—and behavior and process change is always more difficult than technology change. Furthermore, the financial benefits of client virtualization don't really kick in when only a portion of the infrastructure is migrated—because you continue carrying the costs of the help desk, being able to do on-site work, etc.—so in fact, a partial client virtualization implementation actually adds to your costs. It's only when the majority of the client machines are migrated that the cost savings start to accrue.