Jim Lucey over at Exchange team blog posted a response about misleading VMWare guidance for increasing Exchange HA using their technologies.
Here's an excerpt:
"VMware specifically recommends combining their VMware HA solution with Exchange application-aware high availability solution, which's an unsupported configuration. It's important to note that VMware's HA solution only protects from some hardware failures, while Exchange high availability solution protects against both hardware and app failures (including a process for patching guest virtual machines). It's simply reckless for VMware to recommend customers deploy this configuration, while ignoring important Microsoft system requirements and unsupported scenarios. In addition, VMware also seems to gloss over the fact that combining these HA solutions will result in new storage requirements that increase cost and complexity. Considering that a significant focus of Exchange 2010 is reducing storage costs, promoting a strategy that increases storage costs isn't consistent with our customers' requirements.[...]
[…]As we work to test and update guidance pertaining to Exchange running under virtualized environments, our current system requirements are in place to give customers the most reliable email infrastructure possible."