VMware could make more hot add of virtual hardware available before Microsoft:
DHP (Dynamic Hardware Partitioning) features that are coming with Windows Server 2008 (formerly known as Longhorn) allow hot add of hardware without any downtime. It works with Processors, memory, and some PCI express cards. It does not allow removal of hardware without downtime.
An interesting point made at virtualization.info is that VMware could offer these features before Widnows Server 2008 hypervisor is available since it is a part of the base Server OS product.
A video presentation from WINHEC is available that discusses this feature.
And more good info is available at virtualization.info.