VM appliances. The basic standards are there for virtual disk formats, but software vendors have been sluggish to move to this type of distribution. Virtual appliances tend to lack the automatic updates and appliance-like management that make them inexpensive over the long run. Give this one three to five years, though, after which Forrester sees virtual appliances will "radically" simplify vendors' software tsting, since they won't have to account for as many deployment scenarios. That will bring us more stable software that's easier to deploy and manage, on top of faster updates, Forrester says.

VM automation. Most mainstream customers aren't yet ready to hand over control to policy-based automation tools, Forrester says. Within three to five years, IT shops may be ready for this level of automation, after they've finished implementing better IT processes such as change management.

Virtualizing this piece of the puzzle is destined for success, however, given that VM automation tools will allow commodity servers to deliver big-ticket capabilities such as automated disaster recovery and workload prioritization, Forrester says.

And then there are the virtualization technologies that Forrester thinks have hit the "Growth Phase;" i.e., those that have been around long enough that their ecosystems are diverse and their production stories are ample enough for customers to make a decision. These include clustered storage virtualization, VM management, network hardware virtualization, hosted desktop virtualization, local application virtualization, local desktop virtualization and VM hypervisors.

Finally, Forrester pegs four virtualization technologies as being at the "Equilibrium Phase." That means their benefits and limitations are well-documented. At the end of such a phase, the market is "highly consolidated," the customer uptake flattens, and revenues start to slip. Forrester classifies network bandwidth virtualization, hosted application virtualization, in-band storage virtualization and host-based storage virtualization as being in the Equilibrium Phase.