Don't forget to make it Hot with Hot-Add support in vSphere.

Just a tip for those that don’t already know it but vSphere 4 has vcpu and vmem hot add support with hardware version 7. Of course the operating system installed would have to support it. And not all operating systems support both hot add vcpu and vmem. You can find out the supported operating systems here.

Not having to reboot a system in order to add more cpu and/or memory resources is crucial in a production environment but the benefit is no less in dev or stage. If your using vmware templates it will just make sense to configure these options on the templates for better consistency. If your using a current version of Windows and/or Linux operating system you will more than likely be able to use this feature to some degree. Even Windows 7 virtual machines in your VDI environments

Whether the option is supported or not for your giving flavor of operating system will be clearly shown in the “Options” tab under “Memory/CPU Hotplug” when you edit the virtual hardware. The screen shots below shows what you’ll see.