Tom Yager reviewed VMWare ESX for InfoWorld this week. This was a review I wanted to do, but he beat me to it. :-) I think virtualization is a tool that not enough IT managers use yet. I've got ESX installed a couple of Dell 6650 4-way SMP boxes with 16Gb of memory connected to a SAN. This set-up is my virtualization testbed and serves as the platform for study we're doing in my lab. At some point in the not too distant future we hope to have some hard data on the performance trade-offs. Power is one big reason to go virtual that Tom doesn't mention in his article. Data centers are getting denser and hence the power/square foot ration is going up--way up. I believe virtualization on dense servers can reduce overall power requirements and we're trying to gather evidence to support the idea.