Client hypervisors have been around for quite a while in the form of type 2 (hosted) hypervisors. You are probably pretty familiar with type 2 hypervisors - they are things like VMware Server or Microsoft Virtual Server. However, the client hypervisor game recently changed when Citrix released a type 1 (bare metal) hypervisor for client hardware called XenClient. Now, the question is "which type is better?" This question is hotly debated between VMware and Citrix. Brian Madden recently posted an article explaining the pros and cons of each type of hypervisor and the arguments both sides are making. The bottom line is - it depends on your situation.